  In the upstream of the exit ramp of the expressway, the speed limit
difference leads to a significant deceleration of the vehicle in the area
adjacent to the off-ramp. The friction coefficient of the road surface
decreases under rainy weather, and the above deceleration process can easily
lead to sideslip and rollover of the vehicle. Dynamic speed guidance is an
effective way to improve the status quo. Currently, there is an emerging trend
to utilize I2V technology and high-precision map technology for lane level
speed guidance control. This paper presents an optimized joint control strategy
for main line-off-ramp speed guidance, which can adjust the guidance speed in
real time according to the rainfall intensity. At the same time, this paper
designs a progressive deceleration strategy, which works together with the
speed guidance control to ensure the safe deceleration of vehicles. The
simulation results show that the proposed control strategy outperforms the
fixed speed limit control in terms of improving the total traveled time (TTT),
total traveled distance (TTD) and standard deviation of speed (SD). Sensitivity
analysis shows that the proposed control strategy can improve performance with
the increase of the compliance rate of drivers. The speed guidance control
method established in this paper can improve the vehicle operation efficiency
in the off-ramp area of the expressway and reduce the speed difference of each
vehicle in rainy weather, which guarantee the safety of expressway driving in
the rainy day.
