{"data":{"id":"us/40-cfr-1037.527","jurisdiction":"us","citation":"40 CFR 1037.527","heading":"Aerodynamic measurements for vocational vehicles.","body":"This section describes an optional methodology for determining improved aerodynamic drag area, CdA, for vocational vehicles, as described in § 1037.520(m), rather than using the assigned values. A vocational vehicle's aerodynamic performance is based on a DCdA value relative to a baseline vehicle. Determine a DdA value by performing A to B testing as follows:\n(a) Use any of the procedures described in this subpart, with appropriate adjustments, for calculating drag area.\n(b) Determine a baseline CdA value for a vehicle representing a production configuration without the aerodynamic improvement. Repeat this testing and measure CdA for a vehicle with the improved aerodynamic design.\n(c) Use good engineering judgment to perform paired tests that accurately demonstrate the reduction in aerodynamic drag associated with the improved design.\n(d) Measure CdA in m 2 to two decimal places. Calculate DdA by subtracting the drag area for the test vehicle from the drag area for the baseline vehicle.","path":["Title 40—Protection of Environment","CHAPTER I—ENVIRONMENTAL PROTECTION AGENCY","SUBCHAPTER U—AIR POLLUTION CONTROLS","PART 1037—CONTROL OF EMISSIONS FROM NEW HEAVY-DUTY MOTOR VEHICLES","Subpart F—Test and Modeling Procedures"],"source_url":"https://www.ecfr.gov/api/versioner/v1/full/2026-08-25/title-40.xml","current_through":"2026-08-25","vintage":"","retrieved_at":"2026-08-27T02:26:04Z","sha256":"92e52ceba059b5aad70eb6e651c5192881774ce105462971ca5ddf2d59d48729","source_id":"us-cfr","stale":true,"prev":"us/40-cfr-1037.525","next":"us/40-cfr-1037.528"},"notice":"GroundRules: Original legal text. Not legal advice."}