DATE: 06/09/87


TO: Mr. Horton



Thank you for your letter requesting an interpretation of how Standard No. 205, Glazing Materials, would apply to your proposed -head-up display. You described your head-up- display as a system consisting of components located on the instrument panel and windshield that are capable of optically projecting instrument readings so that they appear forward of the lower part of the windshield. You stated that having the readings projected in this manner places them closer to the driver's line of sight and th us allow the driver to view the information more readily and clearly than if the driver had to look for the information on the instrument panel. As discussed below, the agency has concluded that the standard does not prohibit the use of your proposed dis play. Before discussing the substantive question you asked, I want to address your request that the agency not publicly release two types of information contained in your letter. First, you requested the agency to provide confidential treatment to the de tailed description of the technology used in your head-up display. Second, you requested that the agency not disclose the name of your company. You explained in your letter requesting confidential treatment that while the device has been installed on a c ar displayed at a public automobile show, the technical details of the device are not a matter of public knowledge. You subsequently provided thy agency with a copy of your letter in *which the proprietary technical details have been deleted. Because the technical details of your proprietary device have not been publicly disclosed, we will treat the technical details as confidential. In addition, we hill not disclose the name of your company. However, since all of the agency's interpretations are a matt er of public record, we will place a copy of your letter, which has been purged of the confidential information and your company's name, and our response in the agency's public interpretation file.

In the copy of your letter that has been purged of confidential information, you explain that your head-up display uses a small membrane that is attached to the windshield to reflect certain information from the instrument panel. You explained that the a rea of the windshield on which the membrane is attached can meet all of the applicable requirements of Standard No. 205 set for glazing materials used in a windshield, except the requirement that the light transmissions through the glazing material be at least 70 percent. You further explained that the membrane is not opaque, but does have a light transmittance that is less than 70 percent.

Based on your analysis of the requirements of Standard No. 205 and the requirements of the American National Standard -Safety Code for Safety Glazing Materials for Glazing Motor Vehicles Operating on Land Highways, - (ANS Z26) incorporated by reference i n Standard No. 205. -you stated that the 70 percent transmittance requirement does not apply to all window areas. You noted that ANS Z26 specifically provides that the 70 percent light transmittance requirement applies to areas of the glazing that are -r equisite for driving visibility.-In particular, you noted that under the provisions of ANS Z26, a manufacturer can place a shade band on the upper edge of a windshield that has a light transmittance of less than 70 percent. You further notes that Standar d No. 205 and ANS Z26 do not define the boundaries of the shadeband or set a minimum light transmittance level for the glazing materials used in the shadeband. Furthermore, you pointed out that Standard No. 205 and ANS Z26 do not specifically define what areas of the glazing are requisite for driving Visibility.

In support of your position that the area of the windshield affected by your head-up display is not requisite for driving visibility, you noted that the membrane used in the display system -covers a small area of the glazing that is located toward the lo wer left edge of the windshield. To demonstrate that the membrane is not within an area requisite for driving visibility, you examined the effect of the membrane' s location on the ability of the car to comply with the requirements of Standard No. 103, W indshield Defrosting and Defogger, and 104, Windshield wiping and Washing. Standards No. 103 and 104 define three different areas on the windshield and require the wiping system and the defrosting/defogging system of a car to wipe or defrost/defog a pres cribed minimum percentage of each of the three areas. Based on your evaluation of a windshield that has a head-up display membrane, you demonstrated that the area of the windshield covered by the membrane represents only a minimal portion of the three ar eas of the windshield that are required by those standard; to be wiped or defrosted/defogged. You further demonstrated that a car could comply with the requirements of Standard Nos. 107 and 104 even though the membrane slightly project; into the areas re gulated by those standards.

In further support of your position that the head-up display is not located in an area requisite for driving visibility, you provided a comparison of the effects of the head-up display versus the effects of a vehicle's hood design (or unretracted head la mp on a driver's forward and downward visibility. In this comparison, you presented information that measured, from the driver's eyepoint, the location and amount or the driver's forward visibility that would be obstructed by portions of the hood design and by an unretracted head lamp. You then compared the obstructions caused by those design features with the effects of the head-up display on the driver' s visibility. The information you provided shows that a vehicle's hood design or an unretracted hea d lamp can extend as far up in the driver's field of view as the head-up display and provide more obstruction to a driver's forward visibility than the head-up display.

You are correct that while Standard No. 205 and ANS Z26 apply a 70 percent light transmittance requirement to areas of the glazing that are - requisite for driving visibility, - neither Standard No. 205 nor ANS Z26 specifically defines what areas of the glazing are requisite for driving visibility. In fact, as you pointed out in your letter, ANS Z26 specifically provides, in a footnote-to 54.2 of ANS Z26, an exception to the 70 percent light transmittance requirement. The footnote explains that a manufa cturer can provide an area on the glazing, such as a shade band, that has a light transmittance of less than 70 percent as long as the areas requisite for driving visibility have a light transmittance of 70 percent. In interpreting the requisite for driv ing visibility requirement, the agency has not specified a minimum area of the windshield that is requisite for driving visibility. Instead, the agency has said, such as in a letter of February 15, 1974, to Mr. George Nield, that in determining what area s are requisite for driving visibility, the agency will use an approach of determining those areas by reference to vertical heights in relation to the driver's eyes.

(I believe it is important to note that the agency's decision, in the context of shade bands, not to adopt proposed, specific size limits on areas of the windshield which could have less than 70 percent transmittance, was based on the conclusion that suc h a requirement was not necessary because of the voluntary practices of the industry. Thus, although the agency has not adopted a specific requirement, it has been relying on the good faith adherence of the industry to that voluntary practice on shade ba nds. The agency first proposed a limit on the size and light transmittance of shade bands in a notice published in November 1978 (43 FR 51677). In commenting on the notice, several vehicle manufacturers said that such a requirement was not needed since t he industry was voluntarily following a Society of Automotive Engineers Recommended Practice (SAE j100, -Passenger Car Glazing Shade Bands-) that established boundaries for shade bands used on glazed surfaces in passenger cars. As NHTSA explained in a no tice published in January 1981 (46 FR 40), the agency decided to defer further action on the proposed shade band limit until it gathered additional data on the adequacy of the voluntary industry practice.)

After reviewing the information you have submitted, the agency has concluded that the membrane used in your system is located in an area of the glazing that is not requisite for driving visibility. The agency reached this conclusion based on the specific facts of your particular design and the following considerations. The membrane used in system is shall in size, is located near the bottom edge of the glazing area and toward the corner of the glazing area, and although the membrane has a light transmit tance that is less than 70 percent, it is not opaque.

In determining that your head-up display is not located in an area requisite for driving visibility, the agency also considered the effect of the display on a car's ability to meet the requirements of Standard Nos. 103 and 104. Although Standard Nos. 103 and 104 do not define the limits of what areas are requisite for driving visibility, the areas of the windshield covered by the performance requirements of those standards do indicate the agency's concern that, at a minimum, specified portions of those areas of the windshield should be clear during inclement weather to provide the driver with a view of the road. The information provided with your letter shows that a small portion of the head-up display in your vehicle partially falls within the defined areas, but the vehicle still meets the performance requirements of the standards.

Another factor in the agency's decision was the information in your letter showing a comparison of the effects of the membrane versus the effects of a vehicle's hood design or unretracted head lamp on a driver's forward visibility. The information you pr ovided shows that a vehicle's hood design or an unretracted head lamp can intrude as far up into the driver's field of view as the head-up display and provide more obstruction to a driver's forward visibility than the head-up display. This information is an additional indication that the head-up display is not located within an area that is requisite for driving visibility.

Although the agency has concluded that in your particular case your head-up display is not in an area requisite for driving visibility, the agency believes that with the advent of new glazing and other technologies using the windshield, such as the head- up display, it is appropriate to again re-examine the issue of whether to specify the size of the area of the windshield that are requisite for driving visibility. It is apparent that there will be a number of new technologies using the windshield. For e xample, the March 30, 1987 issue of Automotive News carried a news article announcing the development, by PPG Industries and Flight Dynamics, of a 6 inch square holographic display on the windshield.

NHTSA believes that the issues associated with these devices should be addressed in a comprehensive manner. In particular, the agency believes that it needs further information on such issues as whether the areas on the windshield used by these display d evices need to have a lower light transmittance value and, if so, what Chat value should be, where on the windshield the devices can be located, and what limitations should be placed on their size. Addressing these issues in a comprehensive manner by set ting general performance requirements applicable to all such devices, regardless of the technology used, will avoid the inconsistencies and possible design specific limitations that might arise if the agency attempts to provide case-by-case interpretatio ns for each specific design. For all these reasons, NHTSA has concluded that it will address these issues through a comprehensive rulemaking action.

You raised one final issue in your letter. You asked that if the agency Concluded that your head-up display does not comply with Standard No. 205, it should regard the noncompliance as a technical one which does not warrant enforcement. Since the agency has concluded that your head-up display does not violate the requirements of Standard No. 205, the issue is moot.

If you have any further questions, please let me know.


Erika Z. Jones Chief Counsel

December 3, 1986


Erika K. Jones, Esq. Chief Counsel National Highway Traffic Safety Administration 400 7th Street, S.W. Washington, D.C. 20590 Re: Request for Interpretation of FMVSS 205

Dear Ms. Jones:

hereby submits this request for an interpretation of FMVSS 205 (49 C.F.R. S 571:205) as it pertains to display". By letter dated September 17, 1986 to Mr. Stephen Oesch of your office, and in meetings with NHTSA legal and technical personnel, provided the agency with various technical dat a, including design, engineering, and test data, regarding the design and operation of the system. has also provided the agency with a videocassette tape of the operation of a vehicle with the installed, which demonstrated, from the driver's visual perspective, the "real-world" operation of the system. 1/ 1/ requested confidential treatment of such material. As this interpretation request references and discusses such inf ormation, and includes additional confidential technical data, we ask that if confidentiality request be extended to include this letter in its entirety.

The technical documents submitted as attachments to the September 17, 1986 letter to Mr. Oesch were revised in minor respects in subsequent documentation submitted to the agency in our October 21, 1986 meeting with agency legal and technical personnel. For your convenience, this material is attached hereto and referenced herein.

As time is an important factor relative to use of the technology for the model year we would most respectfully request an interpretation by December 3, 1986. On a related note, let me add our expression of appreciation to Messer. Wood and Oesch of your o ffice and the various NHTSA technical personnel who have met with representatives on a timely and cooperative basis to discuss the system.


For the reasons detailed below, requests that your office issue an interpretation that permits use of the technology: We believe that FMVSS 205 does not legally preclude use of the because the does not violate the standard is light transmittance requirements in areas "requisite for driving visibility." M oreover, such an interpretation need not generate any unfavorable "policy" precedent with regard to future interpretation requests.

Alternatively, if you conclude that the does not comply with FMVSS 205, we submit that NHTSA should deem the noncompliance to be a technical noncompliance which -- given the particular characteristics of the HUD, its safety benefits and the absence of an y negative effects on safety -- does not warrant enforcement.


The design and operation of the system is explained in detail in aforementioned submissions, including the videocassette, to the agency. Generally described, the system optically projects readings forward of the windshield. This allows the driver to asce rtain his more readily and clearly than by looking at the dashboard currently used (that is, in systems).

The utilizes a , a membrane attached to the windshield which reflects the readout as transmitted through a The is the only element of the system at issue under FMVSS 205. As currently configured, the is inches horizontally by inches vertically, for a tot al area of square inches, or less than, of the total average windshield area of vehicles.

The combiner is located in of the windshield, to of the driver's direct forward line of vision (about degrees to the left and degrees below the driver' s eye point). 2/ The extent to which this location is out of the line of driving visibility is reflected in the fact that on the models on which the will be used, this location places the at or below the line of sight that extends from the driver's eyes to The combiner has a light transmittance of Based on extensive research and testing, considers that light transmittance is necessary to achieve the optimum reflectance that will permit the -current technology to be visually effective. As test data and the videotape demonstrate, the transmittance, given the size and location of the combiner, does not result in any impairment of driving visibility.


A. FMVSS 205 Does Not Include Use of the For the reasons discussed below, we submit that the complies with FMVSS 205 and with ANSI Z26 as incorporated in FMVSS 205 -- specifically, that the would not violate ANSI Z26's test of 70% light transmittance in areas "requisite for driving visibility. The 70% transmittance test is the only aspect of FMVSS 205 at issue. All other FMVSS 205/ANSI Z26 tests, are met. 2/ All eye range calculations comply with SAE Recommended Practice J941 (Motor Vehicle Driver's Eye Range).

First, the 70% transmittance test of FMVSS 205/ANSI Z26 does not apply to all window areas. Rather, it requires use of safety glazing material with 70% transmittance in areas "requisite for driving visibility." This criterion is not defined in the standa rd itself or by reference. As discussed below, however, it is readily apparent from even a cursory reading of the standard that the "requisite for driving visibility" requirement cannot refer to the entirety of the window areas in passenger cars.

FMVSS 205 on its face makes explicit that the requirement regarding light transmittance applies not to all safety glazing but only to that necessary to driving visibility: The sole purpose stated in the standard relating to light transmittance is "driver visibility" (FMVSS 205 52) : And the standard explicitly recognizes that there are levels at which safety glazing is not requisite for driving visibility: Of course, much of the substance of FMVSS 205 arises from its incorporation by reference of ANSI Z26. Test number two of ANSI Z26, which establishes the 70% light transmission requirement, explicitly provides that its requirement applies to material for use at "levels . . . requisite for driving visibility."

Additionally, it is implicit on the face of ANSI Z26 that some areas of windshield glazing are not "requisite for driving visibility." ANSI Z26 specifies that Glazing materials that. in a, single sheet have--some areas with a light transmittance of less than 70% and are intended for use at levels requisite for driving visibility are to be permanently marked at the edge of the sheet to show what portion of the material may be used at levels requisite for driving visibility. The portion of the glazing materials intended for use at levels requisite for driving visibility must comply within Test No. 2 (the 70% light transmittance tests. (ANSI Z264.2 Item 1, Note l.)

If the entire windshield were considered "requisite for driving visibility", the marking provision quoted above "would be patiently illogical. This provision expressly allows use of a single, continuous piece of windshield glazing with areas of transmitt ance both above and below 70%, so long as the portions used in areas requisite for driving visibility are at or above 70%".

The same conclusion is evident from the SAE recommended practices expressly referencing and utilizing the "requisite for driving visibility" criterion of ANSI Z26. For example, SAE J216 (Electrical Circuits for Passenger Car Glazing) specifies that there is no restriction on the use of electric circuits in passenger-car windows in areas not "requisite for driving visibility. Here again, a construction that all areas of passenge r car windows are "requisite for driving visibility" would plainly be irreconcilable with the explicit content of this SAE provision:

It should also be pointed out here that NHTSA in its approach to shadebands implicitly recognizes that not all areas of windshields are requisite for driving visibility. Shadebands, which obviously do not meet the 70% transmittance requirement, are commo nly used in motor vehicles and are not expressly regulated in NHTSA's motor vehicle safety standards. While ANSI Z26 provides a general marking requirement that applies to shadebands, ANSI Z26 does not define in any way the permissible shadeband area or shadeband transmittance. In fact shadeband areas used by manufacturers vary.

4/ A reading of ANSI Z26 that treats all passenger car window areas as requisite for driving visibility also leads to egregious results. Under such a reading, if a hypothetical were one inch square, with 69% transmittance, and we are located at the very bottom of the windshield, it would nonetheless fail to comply with FMVSS 205/ANSI Z26. A safety standard by law is an agency regulation and therefore may not be construed in a manner that leads to absurd results.

5/ It appears that the agency has never attempted to define the "level requisite for driving visibility" criterion in FMVSS 205/ANSI Z26. Significantly, however, NHTSA has taken the position that this criterion cannot be read pro forma a s applying to co mplete windows or other glazing areas, but must lie considered by reference to "vertical heights in relation to the driver's eyes." See letter from Richard D. Dyson, Assistant Chief Counsel, to George C. Nield, Feb. 15, 1974. We believe use of such an ap proach here convincingly demonstrates that the location is not at a level "requisite for driving visibility" and, indeed, is. This point is discussed at greater length at.

Thus, it is clear under FMVSS 205 and the incorporated ANSI Z26 and by SAE practices and NHTSA' s own policy regarding shadebands that (1) not all areas of windshield glazing are covered by the 70% light transmittance test, but only those areas at levels requisite for driving visibility, and (2) those areas cannot legally be construed as encompassing the entire windshield.

The remaining issue is whether the location of the proposed by is within an area requisite for driving visibility: The standard does not specify the areas "requisite for driving visibility" or define the phrase; thus the agency must look to other pertine nt criteria in determining the scope of the requirement as applicable to the We submit for the reasons discussed below that the only reasonable and legally defensible conclusion based on application of such criteria is that the does not fall within an ar ea "requisite for driving visibility."

In addition, other visibility-related motor vehicle safety standards give strong legal support to the conclusion that the location of the combiner would not be considered critical to driving visibility Reference to FMVSS 104 (windshield wipers and washers) and FMVSS 103 (defrosters and defoggers) provides guidance on what the safety standards generally regard as critical areas of visibility, particularly as pertinent in the context of the Standard 104 specifies essentially a three-part area which must be wiped in whole or in part by the windshield wipers. Standard 103 essentially follows FMVSS 104's "critical area" approach insofar as relevant here: Under FMVSS 104; ninety-nine (99) percent of the smallest and most significant area of viewability (Area C) must be wiped: Ninety-four (94) percent of the intermediate area (Area B) must be wiped, and 80% of the largest area (Area A) must be wiped:

The compliance with FMVSS 104 and 10% visibility area designations is further indication that the presence on the windshield presents no impairment of the driving visibility in terms of the letter or intent of pertinent safety standards dealing with area s of visibility. It is also noteworthy in this regard that as there is no visibility or field-of-view safety standard as such, a that was completely opaque and was placed in an obtrusive position on the dashboard would be entirely permissible. Given this fact, an interpretation that a small, non-obstructing with 6/ In referring to FMVSS 105 and 104, we are not contending that FMVSS 205 is limited or otherwise delineated in scope by FMVSS 105 and 104. We are contending merely that where an agency has not defined broad terms in a regulatory standard as is clearly the case with 205 in this instance it is appropriate indeed, legally necessary where the specific factual context warrants for the standard's provisions to be read in light of other standards wh ich address the same or similar concerns.

only a marginal diminution in light transmittance would be objectionable under FMVSS 205, would be a patiently illogical and indefensible result which can and should be avoided by a reasonable interpretation of FMVSS 205.

It should be evident from the foregoing discussion that the FMVSS 205/ANSI Z26 light transmittance requirement does not legally preclude use of the The "requisite for driving visibility" aspect of the light transmittance test cannot legally be read as re quiring 70% transmittance in the entire windshield area, and indeed contemplates an area which may be substantially less than the entire windshield. Moreover, reference to the actual size and placement of the vehicles, and consideration of the criteria u sed in other visibility-related standards, demonstrates that the neither legally nor practically affects driving visibility.

Additionally, we would submit that not only the size and location of the but also its light transmittance qualities indicate that the does not impair driving visibility. The combiner is not opaque; it has light transmittance, which is only marginally below the 70% requirement for areas requisite for driving visibility. The fact that this diminution of light transmittance in this particular location is of no practical concern is readily apparent from the videotape submitted to NHTSA, which clearly shows that in a variety of conditions the presents no problems regarding visibility.

We believe that it is appropriate to consider the light transmittance characteristics in determining that the size and placement of the do not violate FMVSS 205. To "the extent that in NHTSA's view the demarcation of the area "requisite for driving visibility" is ambiguous or that NHTSA would consider t he location of the to be on the borderline of the area requisite for driving visibility, it is perfectly appropriate indeed, necessary to take into consideration the light transmittance characteristics that would apply in that location.

We emphasize that the contentions advanced above do not require the agency to define or delineate "requisite for driving visibility" in any generally applicable terms. All that is required is that the agency make a determination that given the particular facts involved that is, the location of the its placement at or below the line of sight between the driver's eyes and parts of vehicle structure, the small size of the, and the marginal diminution of light with no apparent visibility impairment the agency has concluded that the 70% transmittance test for areas "requisite for driving visibility" does not preclude use of

B. The System Enhances Motor

Vehicle Safety

The arguments we have presented for an interpretation that permits use of the do not, of course, require NHTSA to assess the safety benefits of the system. However, considering that the ultimate purpose of all safety standards is to ensure safety, we bel ieve the safety benefits and the absence of any negative effects on safety, as discussed below, should be considered by the agency:

The test results submitted to NHTSA show that use of the measurably improves driver safety over the system currently in use. Specifically, the positioning of the in the system closer to the driver's direct line of vision allows the driver to ascertain his vehicle's more readily and more clearly and with less change in direction and distance of focus than is t he case within the. Therefore, use of the system results in the driver's eyes being diverted from the forward road view for a shorter time during his ascertainment of his than with the system, and during that short period he retains better peripheral vis ion of the road than with the system. Although this benefit applies to all drivers, testing establishes that the system offers particular benefits to older drivers, whose recognition and response times generally are slower than those of younger drivers.

Additionally, extensive research and testing have revealed no adverse safety implications of the Assuming NHTSA's approval of the request for a favorable interpretation of FMVSS 205, will be able to certify compliance with all safety standards that conceivably could be implicated by the The safety impli cations of the technology can perhaps be best appreciated by reference to real-world experience. For this reason submitted a videotape of the operation of a equipped vehicle, so that agency officials could see the in operation. believes that such a viewi ng of the provides strong visual evidence of the safety benefits and the absence of any adverse safety implications from this innovative and important technology.

C. There Would Be No Adverse Policy Implications

From A Favorable Interpretation Of FMVSS 205

Some agency officials have expressed concern as to the "precedent" effect or "policy" implications of an interpretation of FMVSS 205 which permits use of the . Although such concerns, strictly speaking, are not legally relevant to a standards interpretation, we respectfully submit that such concerns in any event are not well-founded and can be effectively c ircumscribed through an interpretation which focuses on the highly specific facts presented herein.

Interpretations are, of course, limited to the facts presented in each instance: Indeed, an agency is always free to alter positions or to adopt new positions in interpretations, as the sole touchstone of the validity of an agency's interpretation is its reasonableness.

None of the past interpretations of FMVSS 205 deals with situations even remotely similar to that presented here. The interpretations which apparently have caused the agency some concern involve those dealing with the use of sunscreening devices, includi ng tinted windshields. These interpretations have little bearing on or relevance to the technology. The purpose of the is entirely different, its marginal effect on visibility is purely incidental, and the size and location of the and its level of light transmittance are readily--and favorably--distinguishable. There is simply no credible basis in the wording of FMVSS 205 to believe that the agency could not easily and appropriately interpret FMVSS 205 to disallow sunscreening devices or other troubleso me developments while allowing the technology.

As we have pointed out previously herein, our interpretation request does not require the agency to define the scope of FMVSS 205. The agency need only determine that in light of the "requisite for driving visibility" provision and the unique facts prese nt here (i.e. , purpose of the . the size, location, and substantial transparency), the agency does not believe use of the is legally precluded by FMVSS 205. If the agency is concerned for whatever reason over how an interpretation in the present instanc e would relate to past or future interpretations and wishes to address that concern in the interpretation response, the agency can properly fashion its response in a way that makes clear at a minimum that past interpretation of FMVSS 205 have not present ed facts such as those involved here and that the instant interpretation is strictly limited to the facts presented in the context of the

If The Agency Concludes That The HUD Does Not Comply With FMVSS 205 Non-enforcement Would Be Appropriate We have demonstrated above that ample grounds exist for the agency to permit use of the by finding that the requirements of FMVSS 205 are not violated: If the agency should determine, however, that the does not comply with the standard, we would urge the agency to regard the noncompliance as a technical noncompliance which does not warrant enforcement.

We believe such non-enforcement would clearly be justified: The small size, unobtrusive location, and marginal diminution of light transmittance, taken together with the limitations of FMVSS 2051s 70% light transmittance "requisite for driving visibility " standard, create an extremely cogent set of facts fully justifying non-enforcement on the basis of the agency's exercise of its sound discretion. Moreover, the safety benefits of the system, and the absence of any adverse consequence on safety, are add itional, important factors weighing in favor of permitting use of this significant new technology.

Thank you again for your cooperation. If you have any questions regarding this request, please contact

Attachment Omitted.