engleski

Impact of the penetration rate of intelligent speed adaptation equipment on the effectiveness of variable speed limit control

Today’s roads in urban regions are plagued by heavy congestions. They occur regularly in daily morning and afternoon peak hours, and occasionally as consequence of incidents and special events (fairs, concerts and sport events). To cope with congestions new road infrastructure is being build and services for traffic control from the domain of intelligent transportation systems (ITS) are applied. ITS services include optimization of traffic lights, informing traffic users, real-time vehicle navigation, ramp metering, variable speed limit control (VSLC), etc. Today they use the concept of smart mobility i.e. information exchange between entities. One part of the urban road network where this concept is being currently investigated are urban highways. Such highways connect dense populated urban regions or serve as a bypass of a major city. Its characteristic is that they have many nearby on- and off-ramps. During rush hours congestion builds up around an on-ramp and the resulting traffic jam on the highway can create a shockwave propagating upstream. It closes upstream nearby on- and off-ramps enlarging the traffic jam. Such congestion result also with long queues on on-ramps creating a congestion spill-back effect from the urban highway into the local road network. To prevent this from happening, ramp metering and VSLC are used. Ramp metering limits the amount of vehicles that enter the urban highway by using a special traffic light placed on an on-ramp. Since traffic lights are used, every driver respects this traffic control measure. This is not the case when VSLC is used. Always a certain percentage of drivers exist which do not comply with imposed speed limits reducing the effectiveness of VSLC. To deal with this problem the concept of connected driving is introduced. It consists of a vehicle equipped with an on-board unit (OBU) and vehicle to infrastructure communication abilities, traffic management system with the ability of cooperative control (information exchange between traffic entities), and communication infrastructure. The traffic management system can send the computed speed limit value to the vehicle’s OBU. When this information is received by the OBU, it can inform the driver or can automatically reduce the vehicle’s speed. The latter is called intelligent speed adaptation (ISA). It’s based on the concept that the OBU has limited abilities to alter the driver’s control input. ISA can reduce the vehicle’s speed according to the information obtained from the traffic management system. So it can be ensured that the imposed speed limit will be always respected raising the effectiveness of VSLC. In this paper the impact of the ISA penetration rate on the effectiveness of VSLC is analysed using the CTMSIM macroscopic simulator. A VSLC respect coefficient is defined and added to the CTMSIM simulator enabling simulation of different ISA penetration rates. Obtained results show that raising of the ISA penetration rate raises also the effectiveness of VSLC especially in cases of high traffic demand and that for small penetration rate of ISA (resulting with small driver speed limit compliance) road safety can be significantly deteriorated.

intelligent transportation systems ; intelligent speed adaptation ; variable speed limit control ; CTMSIM

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