Acceleration characteristics of starting vehicles are needed for many transportation analysis and design purposes involving driveways, turning bays, intersecting streets, traffic signals, railroad crossings, simulation software, etc. Constant acceleration is sometimes assumed or AASHTO Green Book values based on piecewise-constant accelerations are sometimes adopted. Yet, continuing research has shown linearly-decreasing acceleration rates better represent both maximum vehicle acceleration capabilities as well as actual motorist behavior. It is not acceleration that is usually constant during speed changes, but the rate of change in acceleration.The evolution of AASHTO acceleration values for design is traced, and the literature is reviewed for pertinent field observations. Linearly-decreasing acceleration (and some deceleration) model parameters are calibrated for various sets of observational and design data.Despite published results from thousands of field measurements, the values selected for design were found to be based mostly on vehicle performance capabilities with conjecture about how much of these capabilities are normally used by drivers. Design accelerations were found to deviate substantially from observed accelerations. At the start of motion, observed accelerations were about 15% faster for passenger cars and 45% faster for SU trucks than design accelerations.As speed increased, observed accelerations dropped 3 to 4 times faster than design accelerations for these vehicles. Observed accelerations for WB-15 trucks began 40% to 75% slower than design accelerations, and were considerably slower than the values in the Green Book for trucks at railroad crossings.
Long ivVoids in the available information base are identified. Linearly-decreasing design acceleration rates for motorists operating different classes of vehicles in different design situations are recommended, and revisions for Green Book parameters and charts are suggested.The recommended acceleration model greatly simplifies acceleration parameters, but implies using different acceleration relationships for different design speeds instead of one for all.Keywords: starting acceleration, design acceleration, motorist acceleration, deceleration Long 1
Acceleration Characteristics of Starting VehiclesAcceleration characteristics of vehicles starting from rest are needed for many transportation analysis and design purposes involving driveways, turning bays, intersecting streets, traffic signals, railroad crossings, simulation software, etc. Constant acceleration is often assumed or piecewise-constant values derived from the AASHTO Green Book (1) are frequently adopted. This paper examines whether the acceleration of vehicles starting from rest is constant, or nearly constant, for various classes of vehicles, and suggests improvements for modeling vehicular acceleration.Several issues are involved. Vehicle acceleration depends upon the type of vehicle, insofar as its size and weight and the engine power available to propel it. This determ...
