Numerical analysis of road capacity

Road capacity refers to the ability of the road to withstand the traffic of vehicles. When the actual traffic volume on the road is less than its capacity, the vehicles on the road are in a state of free driving, with high speed and low traffic density, and the distribution law of headway conforms to the negative exponential distribution, so vehicles can overtake; When the actual traffic volume on the road is close to or equal to its capacity, the vehicles on the road drive along the road at a nearly uniform speed, resulting in the phenomenon of fleet driving, and the headway distribution is close to the average; When the actual traffic volume on the road exceeds its capacity, the density of vehicles on the road increases and the speed decreases, resulting in traffic congestion and congestion. Therefore, in the stage of highway planning and design, the capacity and service level of various highway facilities should be analyzed and evaluated.

The main factors affecting road capacity are road conditions, traffic conditions and traffic environment. Road condition refers to the geometric composition of the road, such as the number of lanes, lane width, lateral width, driving sight distance, longitudinal slope, road surface condition, street conditions along the line, etc. Traffic condition refers to the vehicle composition and distribution characteristics of traffic flow, such as traffic volume, mixed vehicles, pedestrians and non-motor vehicle interference. External traffic environment refers to natural conditions other than road traffic, such as topography, landform, landscape and climate along the line. The combination of these three factors directly affects the driving speed and road capacity.

According to the characteristics of vehicle running state, traffic capacity can be divided into: road traffic capacity, intersection traffic capacity, traffic capacity in the state of confluence and diversion, and traffic capacity in the state of interweaving operation.