A major contributor of fatality in many road crashes is “over speeding”, which makes speed management a vital strategy to address this issue. Effective speed management techniques include setting appropriate speed limits, enhancing enforcement efforts, and raising awareness through educational campaigns. There are different types of speeds, viz. Design Speed, Operating Speed, and Posted Speed Limit.
Need for Posted Speed Limits
Design speeds are generally based on the classification of road types and 85th percentile i.e., speed at or below which 85% of vehicles travel. Currently in India, for setting up of posted speed limits all road-owning authorities have different methods for the highways and urban roads, mostly based on the 85th percentile speed or the direct application of standing order by MoRTH.
Upon reviewing existing guidelines and methodologies, a research gap has been identified regarding the absence of criteria for reviewing the posted speed limit concerning the design speed. Introduce a new approach for establishing appropriate posted speed limits, considering several road-related factors such as land use, vehicle category, road geometry, roadside friction, road markings, vehicle density, composition of vehicles, roadway operations, accident data, average daily traffic values, etc.
Madras Matrix
An in-house comprehensive framework called the ‘Madras Matrix’ is developed to address the identified gaps and establish a systematic method to determine a safe posted speed limit. Various indicators related to the road environment are considered by conducting engineering studies to assess traffic patterns. A speed survey was conducted to determine the 85th percentile speed, and a safety assessment was carried out based on accident history, road classification, and road condition.
‘Madras Matrix’ is a two-fold approach to setting the posted speed limit: perception, which impacts the driver’s behaviour more primarily, and data, which is required for
statistical inference. The score matrix considers five parameters, i.e., land use, road infrastructure, crash data, road features, and traffic classification, to analyse and
evaluate the feasible safe speed limit for a stretch. A total score out of ‘100’ is calculated based on scores allocated to different factors of the five considered parameters. The sum of all the parameter scores will be the value that is used to determine the feasible speed limit.
