D.C. Mun. Regs. r. 18-724
BRAKING STANDARDS TABLE
COLUMN 1 | COLUMN 2 | COLUMN 3 | COLUMN 4 | |
CLASSIFICATION OF VEHICLE | BRAKING FORCE (Percentage of Gross Vehicle or Combination Weight) | DECELERATION (Ft/sec.2) | BRAKE SYSTEM APPLICATION AND BRAKING DISRANCE from initial speed of 20 mph. | |
A | Passenger vehicles with a seating capacity of 10 people or less(including the driver) and not having a gross vehicle rating | 52.8% | 17 | 25 ft |
B1 | All autocycles, motorcycles and motor-driven cycles, and motorized bicycles | 43.5% | 14 | 30 ft |
B2 | Single unit vehicles w/manufacturer's gross vehicle weight of 10,000 pounds or less | 43.5% | 14 | 30 ft |
C1 | Single unit vehicles w/manufacturer's gross weight over 10000 lbs. | 43.5% | 14 | 40 ft |
C2 | Combination of a 2-axde towing vehicle and a trailer with gross trailer wt of 3,000 lbs. or lees | 43.5% | 14 | 40 ft |
C3 | Buses, regardless of the number of axles, without a manufacturer's gross weight rating | 43.5% | 14 | 40 ft |
C4 | All combinations of vehicles in driveway or towaway operations | 43.5% | 14 | 40 ft. |
D | All other vehicles and combinations of vehicles | 43.5% | 14 | 50 ft. |
NOTE: The information set forth in § 724.2 through 724.7 of this section is to be used in understanding and applying the standards for braking performance set forth in the Braking Standards Table in § 724.1. |
There is a definite mathematical relationship between the figures in columns 2 and 3 of the table in § 724.1. If the decelerations set forth in column 3 are divided by 32.2 ft/sec., the column 2 figures will be obtained. (For example, 17 divided by 32.2 gives 52.8%) Column 2 is included in the table because certain brake-testing devices utilize this factor.
The decelerations in column 3 of the table are an indication of the effectiveness of the basic brakes and, as measured in practical brake testing, are the maximum braking decelerations attained at some time during the stop. This deceleration, as measured in brake tests, cannot be used to compute the values in column 4 of the table because it is not sustained at the same rate over the entire period of the stop. The deceleration increases from zero to a maximum during a period of brake-system application and brake-force buildup. Also, other factors may cause the deceleration to decrease after reaching the maximum. The added distance which results because a maximum deceleration is not sustained is included in the figures in column 4 but is not indicated by the usual brake-testing device for checking deceleration.
The values in column 4 of the table and the values in column 3 are not directly related. Column 4 is a definite measure of the overall effectiveness of the braking system, being the distance traveled between the point at which the driver starts to move the braking controls and the point at which the vehicle comes to rest. It includes distance traveled while the brakes are being applied and the distance traveled while the brakes are retarding the vehicle.
The distance traveled during the period of brake system application and brake force build-up varies with vehicle type, being negligible for many passenger cars and greatest for combinations of commercial vehicles. This fact accounts for the variation from twenty-five to fifty feet (25 ft. to 50 ft.) in the numerical values in column 4 for the various classes.
The deceleration value in column 3 of the table is the same for all classifications except passenger vehicles (other than buses) because brakes on vehicles in the B, C, and D classifications are capable with reasonable maintenance of producing the required decelerations as measured by brake-testing devices. A higher deceleration value is warranted for passenger cars by Bureau of Public Roads test data.
Each motor vehicle and combination of vehicles, at all times and under all conditions of loading, upon application of the service brake, shall be capable of the following:
Tests for deceleration and stopping distance shall be made on a substantially level (not to exceed plus or minus one per cent (1%) grade), dry, smooth, hard surface that is free from loose material.
D.C. Mun. Regs. r. 18-724