Secondary crashes on the interstate frequently occur when traffic is queued because of a primary crash and can be quite severe when high-speed vehicles crash into the back of the queue (BOQ). Transportation agencies are aware of this challenge, but there has been limited quantitative data to assess the risk of secondary crashes. This paper examines 47 primary crashes and associated secondary crashes, to quantify the relation between hard braking (HB) events and secondary crashes. These crashes occurred across a diverse cross section of Indiana Interstate locations. Connected Vehicle (CV) trajectories were used to estimate deceleration rates. Trajectories waypoints with deceleration rates greater than or equal to 0.25 g were classified as HB. In total, 762 HB events occurred between the primary and secondary crashes. Only 15 HB events were identified for the control group. An odds ratio statistical measure was used to compare occurrence of HB events and the secondary crash occurrence. The analysis showed it was approximately 62 times more likely that a motorist would experience an HB event when approaching queued traffic associated with a primary crash, in comparison to the control group with free flow conditions. The data and methodologies presented will help agencies incorporate HB into their highway monitoring program and evaluate the impact of incident management and queue protection programs.
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