The speeds at which cars cover individual sections of a route depend on many factors, of which the most important relate to technical conditions in general or on the road surface, speed limits, volumes of traffic and weather conditions. This publication concerns a selected range of issues related to road traffic and is based on research conducted to show periodic changes in vehicle speeds along Polish roads. It represents a step towards increased accuracy of determination of road-traffic conditions, encouraging better prediction and discernment of patterns, as well as greater insight into influential factors. Knowledge of periodic changes in vehicle speeds gains further use in road-traffic modelling, for example at National Traffic Management Centres.
Calculations of the speeds of vehicles covering test-sections of Polish Motorways involved twelve kilometre-long segments of the A1, A4 and A8. Vehicle probe data collected over the four years 2014‑2018 represented the source used in calculating speeds. From within the set of data, further consideration was confined to periods not impacted significantly by such other factors as public holidays, weekends, adverse weather, darkness or maintenance works. The speeds at which vehicles covered the selected sections were calculated, aggregated separately for the light and heavy categories, and then analysed for their daytime and annual variability.
Observed differences in speeds were presented in diagrams, with Fig. 5a for example showing daily variability of speeds achieved by light vehicles under standard working-day conditions. In this case, it is the time around midday that is associated with the lowest values along all sections of Motorway tested. The greatest daily variability in speeds in turn characterises the A8, which in fact as the status of Motorway bypass of Wroclaw, and can thus be treated as a part of that city’s road network. Fig. 5b in turn shows light-vehicle speeds around the year under reference conditions from working days, and indicates a different trend for each section tested. The most marked variability characterizing speeds around the year is noted for the A4 – a Motorway more often serving tourism-related and recreational purposes, an important transit route, and in fact Poland’s only fully-completed Motorway. Where heavy vehicles are concerned, speeds are found to be lower in general, but not greatly different in line with either time of day or month of the year. Almost all sections report a steady average speed of 86 km/h, with only slight fluctuations. Fig. 6 presents the number of journeys on which the study was based. Despite disproportions existing between routes, months and types of vehicle, the samples used in calculations for light vehicles never involved fewer than 100, and those for heavy vehicles a sample size of at least 50.
The first conclusion to be drawn from analysis of the results concerns the inevitable impact on speed of the “traffic volume” factor. However, “traffic vehicular structure” is another factor important in analyses of traffic fluctuations. Were this research to be developed further that would entail further-reaching inference in regard to the nature of traffic and types of trip being made. The research described here can thus be considereda first step in the planning of other, more-accurate measurement campaigns that will require greater preparation in advance, and well as resort to more-specialised equipment. The present homogeneous study nevertheless offers grounds for inferences as to both the nature of the traffic it describes, and the types of trips being made.
A continuation of research would thus extend analyses around the clock (covering 24-hour days rather than just “daytime”), as well as to other days of the week, such as Saturdays and Sundays, to holidays, and even to separate days of the week within the overall set of working days. The number of test-sections might also be increased, and enriched by new types, classes, geometries and locations of routes allowing for fuller inference. In particular, additional locations with Continuous Traffic Measurement Stations would provide for the fuller correlation of vehicle speeds with volumes of traffic. Similarly, filtered datasets factoring in adverse weather conditions, Sun low above the horizon and periods of road maintenance could all provide for more research of a more comprehensive nature.
Dominika Slawik [email@example.com], Politechnika Warszawska, Wydział Geodezji i Kartografii
Jerzy Chmiel [firstname.lastname@example.org], Politechnika Warszawska, Wydział Geodezji i Kartografii
Tomasz Dybicz [email@example.com], Politechnika Warszawska, Wydział Inżynierii Lądowej