Lift-U, Cleatus Lewis
May 29, 2007  [via Email]

Dear Mr. Cannon,

Thank you for the opportunity to respond to the Draft Revisions proposed by the Access Board for the purpose of updating the ADA Accessibility Guidelines for Buses and Vans dated April 11, 2007. In general, we find the majority of the proposed changes to be appropriate and acceptable; however, the proposed 1:8 vehicle ramp slope is idealistic and requires further discussion. Also, ramp deflection tolerance, and lift platform surface and ramp surface gaps/openings need to be addressed. LIFT-U offers the following comments.

Referring to the Access Board’s commentary regarding paragraph (c)(5) of section 1192.23, the statement is made: “Instead of the complicated and confusing slopes tied to floor height, the proposal is to set the maximum slope at 1:8 in all cases, including when deployed to the roadway. This is possible now because of new ramp designs not available when the current guidelines were issued.” With all due respect, LIFT-U must take exception to the Board’s rationale that a maximum slope of 1:8 when a ramp is deployed to the roadway is now possible because of new ramp designs. This simply is not true, at least in the transit bus industry. The majority of low floor transit buses used in fixed-route service have a kneeled step height of 11 inches to 12 inches. Ramps installed in these vehicles typically measure in length from 44 inches to 48 inches, respectively, which corresponds to the maximum slope of 1:4 when deployed to ground level, as presently required in 49 CFR Part 38.23(c)(5). Please refer to the table below and corresponding Figures for graphic illustration. These same ramps, when deployed to most sidewalks result in at least a 1:8 slope.

To my knowledge one of the longest ramps presently available measures 59 inches in length. Even at that length a slope of 1:8 to the roadway is still not feasible. To attain a 1:8 slope with the 59 inch ramp, the bus would have to kneel to a step height of 8.2 inches. Refer to Figure 3 for illustration.

Be advised, in order for ramp access on today’s low floor transit vehicles to achieve the proposed 1:8 slope to the roadway, ramps will effectively have to double in length. Mathematically, flatter slopes require longer ramps or a shorter rise, or a combination of both. Vehicle constraints ultimately limit the envelope size of a ramp assembly, therefore ramp length, and subsequently the ramp slope. Outlined below are several of these constraint issues:

1. Ramps are typically stored within the vehicle. Most are stowed in the vehicle floor. Some slide out from underneath the floor of the vehicle and tilt down. Others fold out. Such a ramp stows in a horizontal position within a recess in the vehicle floor, and is pivoted upward and outward to a downward sloping extended position. In either case, the ramp length is limited by the available space within the vehicle. Transit buses are either 96 inches or 102 inches wide, and constraints in the vestibule area such as the driver’s platform and fare box interfere with longer ramps. Further, the undercarriage of vehicles present interference challenges as well. Chassis structure is a critical element of the vehicle design. Changing structural members to make space for a longer ramp assembly may compromise the structural integrity of the vehicle.

2. Vehicle ground clearance, approach angle, and break-over angle are factors that influence a vehicle’s ride height. Presently, most bus suspensions are capable of kneeling from ride height no more than 3 inches. The ramp length and it’s resulting slope is very much dependent upon the vehicle’s kneeled step height. The lower the step height, the more feasible it is to minimize the ramp slope with a ramp length that fits within the available space. Consequentially, step height is a product of ride height, chassis structure, suspension capabilities (i.e., kneeling or tilting), and tire size or profile.

3. Longer ramps are heavier and thus require more power to reciprocate between stowed and deployed positions. Actuating devices capable of delivering more power are generally larger and require more space in the vehicle.

4. Moreover, longer ramps deploy farther out of the vehicle onto the boarding and alighting surface, which in some cases may prohibit wheelchair access due to unavailable turning space at the outboard end of the deployed ramp.

From a ramp manufacturer’s perspective it seems the simplest solution would be to kneel the bus lower, but without some new suspension technology, that will be extremely difficult for the bus manufacturers to achieve.

LIFT-U has invested considerable engineering time researching the design feasibility of reducing vehicle ramp slopes. Given the present low floor transit vehicle step height and space constraints, we have concluded that a maximum ramp slope of 1:6 to be a more realistic ratio for vehicle and ramp manufacturers’ to accomplish. A 1:6 ramp slope would be a significant improvement from the current 1:4. Therefore, LIFT-U respectfully requests the Access Board amend the maximum ramp slope from the proposed 1:8, to 1:6.

One additional comment with respect to the proposed ramp slope language: “… deployed to roadway” and “… deployed to the intended boarding and alighting areas” is ambiguous given the topographical conditions of roadways and sidewalks, and therefore open to interpretation and opinion. A ramp slope may comply with the Standard at one bus stop, but not at another due to road crown, gradient, or sidewalk slope. There needs to be a standard plane of reference for measuring the ramp slope, such as level ground.

Another element that occurs during passenger boarding and alighting that can exacerbate the ramp slope is deflection. Although 1192.23(c)(1) specifies the design load and safety factor for vehicle ramps, there is no requirement within the specification limiting the deflection of loaded ramps. A ramp may be designed to 1) comply with the design load and safety factors and, 2) when deployed in its unloaded state comply with the slope specification; yet due to design construction and/or ductility of the materials used, when loaded may deflect such that a portion of the ramp significantly exceeds the maximum specified slope. To insure that ramps are sufficiently robust, a deflection tolerance specification should also be included. Interestingly, the Board did include in the vehicle lift portion of the specification, 1192.23(b)(9), a maximum deflection for lift platforms. Therefore, LIFT-U recommends the Board consider augmenting the proposed specification to limit the deflection of loaded ramps to no greater than ¼ inch. While unable to cite a specific precedent to substantiate our suggestion of ¼ inch, it would stand to reason when considering that in a span of 48 inches, a deflection of ¼ inch at mid-span equates to about 1 degree of additional slope at the ramp’s proximal end.

Measuring ramp deflection could be subjective without specifying a test method. One suggestion would be to support the unloaded ramp in a horizontal condition above and parallel to a solid surface. The proximal end of the ramp should be supported in a manner representative of its attachment to the vehicle, whereas the distal end of the ramp should be supported uniformly along its edge. The solid surface must be capable of supporting the test load without deformation. Secure a dial-indicator to the solid surface underneath the ramp at the ramp’s geometric center. Place the 660 pound test pallet (26 inches by 26 inches) at the centroid of the ramp and measure the resultant deflection.

Upon further review, a component missing from the existing specification that was not addressed in the Draft Revisions is in regards to platform surface gaps or opening. The vehicle lift portion of the specification, in 1192.23(b)(7), specifies the maximum allowable gap between 1) the platform surface and raised barriers and, 2) between the lift platform edge and the vehicle floor. With respect to ramps, the only gap requirement in the specification is found in 1192.23(c)(6), which applies to the ramp attachment to the vehicle, limiting the gap there-between. NHTSA in FMVSS 403, paragraph S6.4.4.5 states, “Any opening in that portion of the platform surface that coincides with the unobstructed platform operating volume described in S6.4.2 must prevent passage of a 19mm (0.75 inch) diameter sphere.” Subsequently, LIFT-U recommends the Board consider incorporating surface gap requirements consistent with the NHTSA specification for both vehicle lift platforms and vehicle ramps. In addition, many ramp designs are stowed within a recess in the vehicle vestibule floor. Ramps of this type may also require openings in the recessed surface for operational clearances. When the ramp is deployed, passengers traverse the recessed vestibule surface during boarding and alighting. Thus, LIFT-U also suggests the Board specify maximum vestibule surface gap requirements for ramp equipped vehicles.

For the Boards information, LIFT-U has just developed a new ramp model, the Fold Out Plus – Model LU11, that at a step height of 12 inches deploys to the roadway with a slope of 1:6. The LU11, like its predecessor the LU6, has a rising floor in the interior vestibule. The LU11 rising floor includes a sloped portion, which increases the effective length of the ramp without extending farther outside the vehicle. Furthermore, the stowed ramp package occupies approximately the same envelope within the vehicle floor as the LU6. Figure 4 is a cross-sectional view of LIFT-U’s new ramp, the Fold Out Plus – Model LU11.

Thank you for your consideration and the opportunity to respond to the Board’s Draft Revisions before the formal Notice of Proposed Rulemaking (NPRM) is issued.

Regards,

Cleatus Lewis
Engineering Manager
LIFT-U

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Figure 4