Motorway travel time estimation: A hybrid model, considering increased detector spacing

Travel time is one of the indicators to quantify congestion and is an important parameter for the development and evaluation of strategies to mitigate congestion and its detrimental environmental and social impacts. Travel time estimation and prediction on motorways has long been a topic of research. Prediction modelling generally assumes that the estimation is perfect. If the estimation is garbage, then no matter how good is the prediction modelling, prediction will also be garbage. Models have been proposed to estimate travel time from loop detector data. Generally, detectors are closely spaced (say 500 m) and travel time can be estimated accurately. However, detectors are not always perfect, and even during normal running conditions few detectors are not working, resulting in increase in the spacing between the functional detectors. Under such conditions, error in the travel time estimation is significantly large and generally unacceptable. This research evaluates the in-practice travel time estimation model under different scenarios. Potential sources of errors (such as detector error, congestion build-up and dissipation, detector location) are identified. Thereafter, a hybrid model that can be easily adopted by motorway operators for time travel time estimation with acceptable accuracy limits is proposed and tested using simulation.