Probabilistic risk assessment for pedestrian–vehicle collision considering uncertainties of pedestrian mobility

Objectives: The uncertainties of pedestrian mobility are important factors affecting the accuracy and robustness of an active pedestrian protection system. This study is to provide the means for probabilistic risk evaluation of pedestrian–vehicle collision by counting the uncertainties in pedestrian motion.

Method: The pedestrian is modeled by a first-order Markov model to characterize the stochastic properties in mobility according to field experiments of pedestrians crossing an uncontrolled road. Based on the assumption of Gaussian distribution, unscented transformation (UT) is employed to predict the collision risk probability with the symmetric σ-set constructed on the basis of discrete trajectory simulation. Simulation experiments were carried out with 10,000 Monte Carlo (MC) simulations as the reference.

Results: The probability density distributions of time-to-collision, minimal distance, and collision probability estimated by UT coincide with the reference ones under various vehicle–pedestrian conflict scenarios, and the maximal deviation of collision probability from the reference is 5.33%. The UT method is about 600 times faster than the MC method (10,000 runs), which means that the proposed method has the potential for online application.

Conclusions: This article presents an effective and efficient algorithm to estimate the collision probability by using a UT method to solve the nonlinear transformation of uncertainties in pedestrian motion. Simulation results show that the UT-based method achieves accurate collision probability estimation and higher computation efficiency than MC and provides more valuable information concerning collision avoidance than the deterministic methods in the design of a pedestrian collision avoidance system.     

Using consequence – based hazard zone assessment for effective evacuation planning of vulnerable settlements along hazmat transport corridors through industrial city of Surat in western India

Following a toxic hazmat release, decisions need to be made vis-a-vis a safe evacuation distance for population along the transportation route, or whether to shelter-in-place if there is insufficient time to conduct an evacuation. The first responder may have to take these decisions through a quick estimation of the Initial Isolation Zone (IIZ) and protective action distances based on assumed rate of releases. Real-time evacuation planning models could be used for effective evacuation purposes. However, factors that usually were taken into account include weather conditions, population density, time of day, and uncertainty about the chemicals involved and/or the accumulating concentrations in public areas. Emergency planning including evacuation in India is generally in line with UNEP's APELL (Awareness and Preparedness for Emergencies at Local Level) methodology. However, quantitative risk based assessment is catching up particularly in large industrial zones. The paper highlights a case study of the evaluation of identified seven critical evacuation planning zones along three highway study routes in and around the industrial city of Surat in western India. The elapsed time after a release is estimated through ALOHA and evacuation travel time estimates are made for each zone. For identified scenarios, evacuation of IIZ, generally comprising of road side population, is effectively possible in six out of seven identified emergency planning zones except in zone-7, where certain people would still be exposed, as full evacuation may not be achieved. However, shelter-in-place would be advisable for population residing in permanent settlements within the protective action zone.