Dynamic speed limit control to resolve shock waves on freeways : Field test results of the SPECIALIST algorithm

We present the real-world test of the SPECIALIST algorithm in which dynamic speed limits were used to resolve shock waves on freeways. The real-world test was performed in the period September 2009–February 2010 on a 14 km long stretch on the Dutch A12 freeway. For the evaluation of the algorithm various performance measures were determined for each activation of the speed limits. The results show that the SPECIALIST algorithm can resolve shock waves in nearly 80% of the cases when the algorithm activated for shock waves. However, in approximately 50% of the activations the algorithm activated for jam types other than shock waves, in which case the effectivity was 40– 50%. Due to the tuning the stability of the traffic flow could be significantly improved, and the number of average activations per day was increased from 1.5 to 2.9 activations per day. The SPECIALIST algorithm was not only evaluated for traffic performance, but also for the correctness of the algorithm for real traffic in terms of expected qualitative behavior. Although the general operation of the algorithm is according to the theoretical expectations, some points for further improvements are identified during the test

Freeway lab: testing dynamic speed limits

This paper presents the Dynamic Speed Limit (DSL) experiment that took place in June 2013 on the last 13 km stretch of the B-23 freeway accessing the city of Barcelona (Spain). The DSL system installed on that freeway in addition to the high density of surveillance equipment available makes this stretch a suitable highway lab. The objective of the experiment was to construct a comprehensive database of traffic engineering variables on a freeway site when different speed limits apply. Special attention was paid to ensure similar demand conditions. The experiment included the modification of the speed limits on a freeway segment making use of dynamic signals. Detailed measurements of vehicle counts, speeds, occupancies, lane changing maneuvers and travel times were taken. These simultaneous measurements obtained from very different types of monitoring equipment have been grouped into a single database. These include measurements from inductive loop detectors, radar, ultrasound and passive infrared non-intrusive traffic detectors, TV cameras and license plate recognition devices. The potential of this multi-source database is huge. For instance, a preliminary analysis empirically proves that drivers’ compliance with dynamic speed limits is very limited, unless speed enforcement devices are present. In addition, it is also proved that lane changing rates increase together with the occupancy level of the freeway. This comprehensive DSL database, unique in its nature, is made publicly available to the whole research community [Link], [1] in order to use up all its information. The present paper aims to present in detail this DSL experiment and its results and to contribute in the dissemination of the resulting database. This will facilitate its analysis to any interested researcher, and would lead to a better understanding of the causes and effects of DSL strategies on freeways.Postprint (published version

New concepts for urban highways control

In recent decades a significant increase in traffic demand has occurred. This trend is especially present in dense populated areas where daily traffic congestions during rush hours occur regularly. Congestions are significant in road traffic where they can simultaneously reduce public transportation level of service (LoS) also. As consequence, even more people are using their car additionally increasing the congestion problem. Classic solution for solving the road traffic congestion problem is infrastructure build up. Today’s dense urban areas mostly do not allow this approach because of the lack of available building space. More advanced road traffic control solutions from the domain of intelligent transportation systems (ITS) are being more and more applied to optimally use the existing infrastructure (Papageorgiou et al., 2003.). Such solutions include coordination between several consecutive crossroads, dynamic traffic assignment, driver informing systems, etc. One of the ITS application areas is related to urban highways which present a class of highways used as a city bypass or are just passing a dense urban are. Their main characteristic is that they have a larger number of on- and off-ramps often placed at small distances. Due to the small distance, mutual on-ramp influence can occur enlarging the problems of daily congestions and associated decrease of highway LoS. In order to prevent the appearance of traffic standstill or to reduce its duration control approaches as ramp metering and variable speed limit control (VSLC) are being applied (Hegyi et al., 2010.). In recent years, new cooperative concepts between several on-ramps and VSLC are used as a combined urban highway control system (Ghods et al., 2007.). This paper presents a new learning based cooperative ramp metering strategy in which several well-known ramp metering strategies (ALIENA, SWARM, HERO) are used to create a learning set for an ANFIS (Gregurić et al., 2013.) based control structure. Optimal ramp metering values are obtained for a wide range of traffic demand on the urban highway and belonging on-ramps. Optimal ramp metering values for specific traffic demand characteristics obtained from most suitable ramp metering strategies are integrated into only one control strategy. Thus, the need of applying several ramp metering strategies and switching between them is avoided. Additionally, cooperation between VSLC and vehicle control by an on-board unit is described and a discussion about possible implementation is given. Proposed cooperative urban highway management approach is tested in simulations using the city of Zagreb bypass as case study. For simulation, the macroscopic highway traffic simulator CTMsim (Kurzhanskiy et al., 2008.) is used. Used CTMsim simulator augmented to enable simulation of VSLC and cooperative ramp metering approaches

Effects of low speed limits on freeway traffic flow

Recent years have seen a renewed interest in Variable Speed Limit (VSL) strategies. New opportunities for VSL as a freeway metering mechanism or a homogenization scheme to reduce speed differences and lane changing maneuvers are being explored. This paper examines both the macroscopic and microscopic effects of different speed limits on a traffic stream, especially when adopting low speed limits. To that end, data from a VSL experiment carried out on a freeway in Spain are used. Data include vehicle counts, speeds and occupancy per lane, as well as lane changing rates for three days, each with a different fixed speed limit (80 km/h, 60 km/h, and 40km/h). Results reveal some of the mechanisms through which VSL affects traffic performance, specifically the flow and speed distribution across lanes, as well as the ensuing lane changing maneuvers. It is confirmed that the lower the speed limit, the higher the occupancy to achieve a given flow. This result has been observed even for relatively high flows and low speed limits. For instance, a stable flow of 1942 veh/h/lane has been measured with the 40 km/h speed limit in force. The corresponding occupancy was 33%, doubling the typical occupancy for this flow in the absence of speed limits. This means that VSL strategies aiming to restrict the mainline flow on a freeway by using low speed limits will need to be applied carefully, avoiding conditions as the ones presented here, where speed limits have a reduced ability to limit flows. On the other hand, VSL strategies trying to get the most from the increased vehicle storage capacity of freeways under low speed limits might be rather promising. Additionally, results show that lower speed limits increase the speed differences across lanes for moderate demands. This, in turn, also increases the lane changing rate. This means that VSL strategies aiming to homogenize traffic and reduce lane changing activity might not be successful when adopting such low speed limits. In contrast, lower speed limits widen the range of flows under uniform lane flow distributions, so that, even for moderate to low demands, the under-utilization of any lane is avoided. These findings are useful for the development of better traffic models that are able to emulate these effects. Moreover, they are crucial for the implementation and assessment of VSL strategies and other traffic control algorithms.Peer ReviewedPostprint (published version

Dynamic speed limit control to resolve shock waves on freeways - Field test results of the SPECIALIST algorithm

We present the real-world test of the SPECIALIST algorithm in which dynamic speed limits were used to resolve shock waves on freeways. The real-world test was performed in the period September 2009–February 2010 on a 14 km long stretch on the Dutch A12 freeway. For the evaluation of the algorithm various performance measures were determined for each activation of the speed limits. The results show that the SPECIALIST algorithm can resolve shock waves in nearly 80% of the cases when the algorithm activated for shock waves. However, in approximately 50% of the activations the algorithm activated for jam types other than shock waves, in which case the effectivity was 40– 50%. Due to the tuning the stability of the traffic flow could be significantly improved, and the number of average activations per day was increased from 1.5 to 2.9 activations per day. The SPECIALIST algorithm was not only evaluated for traffic performance, but also for the correctness of the algorithm for real traffic in terms of expected qualitative behavior. Although the general operation of the algorithm is according to the theoretical expectations, some points for further improvements are identified during the test

Variable Speed Limit Control on Urban Motorways based on Decision Logic Trees

Oko velikih gradova grade se obilaznice čija je namjena rasteretiti urbanu cestovnu mrežu unutar grada. Takve obilaznice se najčešće svode na urbane autoceste s većim brojem ulaznih i izlaznih rampi. Mjesta gdje se nalaze ulazne i izlazne rampe sklona su pojavljivanju prometnih zastoja. Njihovo pojavljivanje se može smanjiti ili u potpunosti spriječiti prikladnim upravljanjem ograničenjem brzine vozila glavnog toka urbane autoceste. U radu su opisani problemi upravljanja prometom na urbanim autocestama, objašnjeni su pristupi za upravljanje ograničenjem brzine, analizirane su mogućnosti primjene logičkog stabla odlučivanja za upravljanje promjenjivim ograničenjem brzine, izrađen je model dionice urbane autoceste i iskorišteni su postojeći prometni podaci za simulaciju modelirane dionice autoceste uz korištenje simulatora VISSIM.Bypasses are being built around big cities to disburden the urban road network within the city. Such bypasses are usually confined as urban motorways with a large number of entry and exit ramps. Traffic jams are prone to occur in places where the entry and exit ramps are. Occurrence of traffic jams can be reduced or completely prevented by the appropriate use of vehicle speed limit control on the main road of the urban motorway. In this thesis, problems of traffic management on urban motorways are discussed, approaches for speed limit control are explained, the possibilities of applying the decision logic tree for variable speed limit control are analyzed, a model of an urban motorway stretch was made and the existing traffic data were used for simulation of the modeled motorway section using the VISSIM simulator

Variable Speed Limit Control on Urban Motorways based on Decision Logic Trees

Oko velikih gradova grade se obilaznice čija je namjena rasteretiti urbanu cestovnu mrežu unutar grada. Takve obilaznice se najčešće svode na urbane autoceste s većim brojem ulaznih i izlaznih rampi. Mjesta gdje se nalaze ulazne i izlazne rampe sklona su pojavljivanju prometnih zastoja. Njihovo pojavljivanje se može smanjiti ili u potpunosti spriječiti prikladnim upravljanjem ograničenjem brzine vozila glavnog toka urbane autoceste. U radu su opisani problemi upravljanja prometom na urbanim autocestama, objašnjeni su pristupi za upravljanje ograničenjem brzine, analizirane su mogućnosti primjene logičkog stabla odlučivanja za upravljanje promjenjivim ograničenjem brzine, izrađen je model dionice urbane autoceste i iskorišteni su postojeći prometni podaci za simulaciju modelirane dionice autoceste uz korištenje simulatora VISSIM.Bypasses are being built around big cities to disburden the urban road network within the city. Such bypasses are usually confined as urban motorways with a large number of entry and exit ramps. Traffic jams are prone to occur in places where the entry and exit ramps are. Occurrence of traffic jams can be reduced or completely prevented by the appropriate use of vehicle speed limit control on the main road of the urban motorway. In this thesis, problems of traffic management on urban motorways are discussed, approaches for speed limit control are explained, the possibilities of applying the decision logic tree for variable speed limit control are analyzed, a model of an urban motorway stretch was made and the existing traffic data were used for simulation of the modeled motorway section using the VISSIM simulator

Speed Distribution Based Approach for Shockwave Detection in a Connected Driving Environment

One of the key advantages of connectivity in highway environments is the possibility of shockwave detection at the onset of formation, which can provide more flexibility in mitigating congestion. Past research used data from radar guns and loop detectors to show that a rapid increase in speed variance could be an indicator of shockwave formation. This paper investigates the possibility of utilizing connected vehicles data and vehicle trajectory data to determine if any increase in speed variance over distances could be an indicator of shockwave formation. Moreover, the effects of limited information in a connected driving environment on shockwave detection based on speed variance were explored. Two datasets were evaluated: I-5 Connected Vehicles dataset and NGSIM US 101 dataset. Six segments analyzed in the I-5 dataset showed that a jump in speed variance could detect congestion earlier than looking at average speed alone. The NGSIM US 101 scenarios of 100, 50 and 10 percent market penetration rates (MPRs) were analyzed assuming 100, 80, and 50 percent of speed data were received at each time step. For MPRs of 100 and 50 percent, speed variance was able to identify the six shockwaves in the dataset. The RMSE, calculated for various MPRs, showed an inverse relationship to MPR. The impact of misinformation from potential cyberattacks or equipment malfunctions was also tested on the US 101 dataset. Speed variance was more robust than average speed when speeds were reported either higher or lower than actual speeds. When speeds were falsely reported as a combination of higher and lower than actual speeds, variance continually increased, though a jump in variance was still an indication of shockwave formation. When incorrect speeds were reported for only a high variance interval by 1-5 mph and 5-10 mph, speed variance remained a strong indicator of congestion formation. Analyzing the US 101 dataset with larger distance intervals, by individual lanes, and by different lane aggregations improved variance based shockwave detection reliability. Shockwaves detected earlier and more reliably can delay shockwave propagation and further reduce negative impacts on safety, performance, and emissions