Research On Traffic Flow Characteristic Parameters Of Urban Road Section In Adverse Weather Conditions

With the rapid growth of car-owners in mega cities, urban traffic problemsbecome increasingly prominent. Insufficient capacity and poor efficiency of urbantransportation system resulted from adverse weather has been taken into account bythe management department and the public. This research focused on the methods ofquantifying the impact of adverse weather (rain and snow) on the road traffic flowbehavior, to guide the relevant departments to develop effective managementmeasures and to improve the traffic participants’ travel efficiency and reliability.Taking Beijing expressways and arterial road as the main study objects,relationships between weather conditions and the fundamental traffic flow parameterswere analyzed with meteorological data captured in light rain, moderate rain, snow,and moderate snow condition separately. Based on fixed detector data andsurveillance video, the study selected10minutes as the time interval for the analysis,and applied the independent-samples T-test to prove that the difference of transportfacility type, road alignment design, section position and number of lanes resulted indifferent influence on traffic flow parameters. Then various sections were used todescribe the traffic flow characteristics during different weather conditions. Nonlinearregression models were calibrated to estimate the capacity and speed at capacity. Andsingle-factor regression analysis was used to compare the free-flow speed in differentweather conditions.The results showed that expressway traffic capacity with varying degrees ofreduction was caused by complicated road alignment, more lanes and trafficinterference which were the most significant influence factors. Traffic flow ofexpressways on snowy days depends primarily on travel demand reduction of privatecars. During light rain, moderate rain and snow weather, max-flow rate of the arterialroad was reduced by7%,17%and48%, respectively.Free-flow speed of the expressway was affected by snow weather moresignificantly than rainy weather. In the same rainfall or snowfall condition, roadsection with more lanes has a larger free-flow speed reduction. Free-flow speed of thearterial road was reduced less than4%in light rain and moderate rain weather, and thereduction reached44%in snowy weather.The research results can provide a useful reference for urban traffic managementunder adverse weather conditions.