The BPR model was used to release the law between the characters of parking vehicle and speed of the main road. This paper focuses on the rightmost lane on the main road at the sections of off-street parking access in the city. An impedance function model describing the off-street parking vehicle enters or not was established through the analysis of theory and specific cases based on parameters. Some conclusions can been drawn as follows:firstly, speed of the rightmost vehicle is only related to its flow and proportion of the lane been utilized is only 0.384, while there is no off-street parking vehicle; secondly, speed of the rightmost vehicle is related to the influence time, frequency of parking, deceleration distance and its flow, while the off-street parking vehicle entry into the access. Meanwhile, sensitivity analysis of influence of relative factor on the speed of the social vehicles was conducted. Results show that the parking vehicle's deceleration distance is contrast to the average speed and it's influence time is in proportion to the average speed, while the off-street parking vehicle affected the vehicles on the rightmost lane. Moreover, the social vehicles would be deeply affected by the off-street parking vehicle, while the deceleration distance is less than 10 m.