Parameters influencing probe vehicle based travel time estimation accuracy

Floating Car Data (FCD) is becoming a more and more popular technique for travel time measurements in road networks. Nevertheless, FCD is a sampling technique which requires controlling the statistical properties of link travel times to obtain accurate estimations. Based on microsimulation outputs, this paper shows which parameters play a key role in the travel time estimation accuracy, particularly in the case of urban networks. Among them, aggregation period and link definition are the most critical ones. They must be properly chosen according to the equipped vehicles ratio

Floating Car Data: travel time estimation methods using micro-simulation evaluation

Floating Car Data (FCD) is becoming a more and more popular technique for travel time measurements in road networks. Nevertheless, FCD is a sampling technique which requires controlling the statistical properties of link travel times to obtain accurate estimations. Based on microsimulation outputs, this paper shows which parameters play a key role in the travel time estimation accuracy, particularly in the case of urban networks. Among them, aggregation period and link definition are the most critical ones. They must be properly chosen according to the equipped vehicles ratio

Link travel time estimation with probe vehicles in signalised networks

One of the more useful dynamic data used by ATIS (Advanced Traveller Information Systems) and ATMS (Advanced Traffic Management Systems) applications is the link travel time, in particular for the DRGS (Dynamic Route Guidance Systems) case. Among the different methods for collecting these data, the use of probe vehicles is one of the most efficient and promising method. However, accuracy issues have to be solved, above all, from the statistical point of view. This paper presents an analyse of the individual link travel time records distribution shape of a typical urban network link. The influence of this analysis on the probe vehicles-based estimation accuracy is also described. A division of the overall records in sub-samples according to the upstream and downstream link used by the vehicles is proposed. Advantages and disadvantages of this approach are commented. The necessity of integrating the link travel time estimation accuracy in a path context instead of treating it as an individual entity is demonstrated. Finally, some conclusions are given and further research needs are highlighted

PAPABILES Simulation-based evaluation of the impact of telematics in the Lausanne area: a pilot study

At the present time, variable-message signs (VMS) and variable speed-limit signs are in frequent use for traffic control, especially along urban motorways. The Lausanne by-pass is partially equipped with these and should be fully equipped in the near future. This study is made to evaluate the effects of such systems, either on the efficiency of the road network or the security of its users. The PAPABILES pilot-study deals with the evaluation of the potential effects of such control systems on the performance and safety of the network, using a stateof- the-art simulation tool (MITSIM), developed at the Massachusetts Institute of Technology. In this paper, we present the scenarios that have been tested and comment on the results. Preliminary analysis of the impact of variable speed limit signs made it possible to emphasize the following elements: a) The reduction of the speed limit in the case of high-flow scenarios did not produce a significant increase in the performance of the motorway network, usually limited to 120 km/h. For limitations lower than 100 km/h, it actually seems to decrease. Admittedly, some results tend to show a slight improvement of the performance for speeds around 105 km/h. However, the magnitude of these improvements is too low to justify the installation of such equipment for the sole purpose of increasing the performance of the network. b) About the question of road-users' safety in the presence of high flow, a lower speed limit decreases the probability and the severity of an accident when the traffic breaks down from a normal regime to a congested regime. As mentioned above, this safety improvement does not significantly affect the system's performance in terms of throughput. c) In the case of an incident that notably reduces the capacity of the motorway, simulations carried out up to now show that the application of various speed limitation scenarios does not improve the performance of the network. The capacity of the network is governed by the capacity at the incident location and the actual speed is already below the limitation. Again, the role of speed limitation is more beneficial for safety than throughput. We emphasize that, due to the limited calibration of the model, the results must be interpreted with care. We believe that their interpretation is valid, but that their actual impact must be analyzed in more detail. This will be achieved in subsequent phases of the project

Self supplied navigation systems: microsimulation-based performance assessment

The self-supplied navigation concept is based on the combination of the floating car data technique and the dynamic route guidance service in the same vehicles. The gains obtained by the users of such system are, obviously, closely related to the percentage of equipped vehicles. This study shows concretely this relation relying on the use of a large scale microsimulator urban model, the Lausanne city case. Finally, limitations due to the fact that the same vehicles are providing and exploiting the traffic information are clearly emphasized

Route choice relevance in complex urban network micro- simulation models

In dynamic models, like microsimulation, dynamic traffic assignment is based on the use of traffic conditions measured during the simulation process in order to keep o sort of equilibrium between demand and supply. Route choices are consequently done by knowing the traffic conditions of the day. This paper suggest another model, more realistic, based on an historical drivers knowledge obtained by an iterative process. This new model, splitting drivers in different knowledge categories, allows more relevant ATIS evaluation

Historical based traffic assignment in microsimulation for advanced traveller information systems assessments

In dynamic models, like microsimulation, dynamic traffic assignment is based on the use of traffic conditions measured during the simulation process in order to keep o sort of equilibrium between demand and supply. Route choices are consequently done by knowing the traffic conditions of the day. This paper suggest another model, more realistic, based on an historical drivers knowledge obtained by an iterative process. This new model, splitting drivers in different knowledge categories, allows more relevant ATIS evaluation

The importance of computing intermodal roundtrips in multimodal guidance systems

Most of the current intermodal traveller information applications still consider one-way journeys only. For the calculation of a roundtrip two simple one-way trips are taken into account. However, most of the journeys do not consist of simple one-way trips, as a traveller usually returns to the starting point (home, office for business trips, etc.). Also, arc cost – travel time in general – tend to be time dependent, which means that the cost of the optimum roundtrip is not necessarily the double of the cost of the optimum one-way trip. The diverse arc cost values can be based on dynamic and/or historic data. A lot of effort is spent in order to obtain and store this type of data, which is necessary for describing real-time traffic states and to make forecasts. So the next step is to make better use of this data by integrating them into the calculation of trips that take place in the future. A multimodal information service usually works as follows: The traveller indicates his starting point, his destination and the desired time of departure or arrival. The system then computes the optimum trips for private modes (car, bicycle, etc.) and public transport (all modes). It is up to the user to compare the different possibilities and to decide which one to take. Dynamic data are integrated where available. The possibility of switching between different transportation modes during the trip is rarely offered. The main reasons are the difference in the models (different graphic levels are used for different modes) and the different parameters for describing the arc cost for the different modes. Roundtrips can usually be computed for certain modes, especially for public transport, which relies on static timetable data. In this case, the intermodality is limited to some or several public transport modes of a certain region. More and more service providers offer the possibility to optimise a door-to-door trip, taking into account the time necessary to reach the first transport mode used, as well as the time to reach the destination from the last stop. This paper describes the importance of computing entire intermodal roundtrips rather than two one-way trips, as arc cost tend to vary depending on different parameters (time of the day, special events, etc.). Having more and more dynamic and historic data at hand, it should be used to the maximum possible, in order to optimise mobility habits. Computing intermodal roundtrips also means taking into account several constraints that may arise on the way, like the dependence on a certain mode or leaving behind a private vehicle at certain nodes of the network. The main constraints are pointed out, along with their importance for the calculation

PAPABILES Simulation-based evaluation of the impact of telematics in the Lausanne area: a pilot study. Phase 2: third lane and ramp metering

T hi s st udy f ollows the f irst phase of the PAPABI L ES project of which the purpose was to judge t he eff i ci ency of vari abl e speed lim i ts on the sect ion of the A1 m ot or way ranging bet ween the junct ion of Mor ges West and the Ecublens interchange. The results had shown that this tr af fi c m anagem ent tool i s of i nt er est but di d not real ly all ow sol vi ng the pr obl em of chr oni c congest ion obser ved i n the Mor ges East j uncti on zone. T hi s second phase of the PAPABI L ES pr oj ect proposes t o evaluate and to compare t wo types of r esponse to thi s pr obl em . T he fir st consist s in pr olonging the acceler at ion lane of the Mor ges E ast juncti on up to the Ecublens inter change, thus al lowi ng the traff i c to fl ow out on 3 lanes bet ween these t wo points. T he second, typical appli cati on of t he IT S field, i s the i mpl antati on of a r am p met er i ng on the Morges-east j uncti on ramp T hese eval uat ions were carr ied out by usi ng the microscopi c sim ul at or AI MSUN, a t ool devel - oped at the Pol yt echni c Uni versi ty of Cat al unya, i n S pai n. T he result s show that the const r ucti on of a thir d lane between the Mor ges East junct ion and the E cubl ens i nt erchange woul d al low decr easi ng tr avel ti mes on the studi ed secti on of al most 27 % and thi s in the case of ver y hi gh tr aff ic fl ows. This incr ease of the net work perf or m ance is the r esul t of the addit i on of two posi ti ve im pacts generated by the presence of the thir d lane, the suppr ession of the bot tl eneck at the exit of the Morges East juncti on and the incr ease in fl ui di t y and aver age speed. T he result s also show that ramp meter ing does not all ow avoi ding the presence of congesti on at the Mor ges East juncti on. Never theless, i t m akes possibl e the decrease of the pr opagat i on upstr eam of the j unct i on and especiall y t he durati on in ti me. Ram p met er ing also makes possibl e to reduce in a si gnif i cant way the del ays generated by the presence of an acci dent located downstr eam of the junction. This decr ease is part icularl y im - por tant for medium demand f lows (whi ch do not involve congestion due to a lack of capacity at t he Mor ges East j uncti on) where reducti ons of 40 % wer e recor ded. T hi s st udy made it possi ble to concr etely eval uat e the improvem ents that can be achieved by t wo sol uti ons of com pl et ely dif f er ent charact eri st i cs concer ni ng i mpor tance, cost and impl icat ion. It also all owed com pari ng two types of str ategi es answer i ng a pr oblem of capacit y lack: t he i ncr ease of t he suppl y or a bet ter dem and m anagem ent