Abstarct: As the traffic flow increases, the probability of accidents increases. Accidents have negative effects on traffic characteristics. Accidents result in reduced speed, increased congestion, reduced flow, and reduced road capacity. The purpose of this research is to investigate the effect of one-lane and two-lane closures on traffic characteristics and shockwaves developed under its influence on the separated three-lane highway(Saffe Highway). The data used in this research was taken from traffic videos. In this research, the LWR shockwave model is presented baxsed on different speed-density relationships. Then the numerical solution of the shockwave model is performed baxsed on the Lax–Friedrichs scheme to investigate the effects of one-lane and two-lane closures. The obtained results show that two-lane closure has more effects on traffic characteristics than one-lane closure. one-lane and two-lane closures have reduced the capacity of the highway by 29 and 61 percent, respectively. In order to compare shockwave models caused by speed-density relationships, root mean square error(RMSE), mean absolute error(MAE) and relative error(RE) have been used. With the comparison made, the lowest amount of errors mentioned for one lane and two lane closures for shockwave models is baxsed on the Underwood speed-density relationship with Taylor series expansion. The relative error of the shockwave models baxsed on the Underwood speed-density relationship with Taylor series expansion for one lane and two lane Closures are 4.24% and 6.28%, respectively. Therefore, the shockwave model baxsed on the Underwood speed-density relationship with Taylor series expansion can estimate traffic characteristics and shockwaves better than other models.