Well, the obvious answer is for the drama, but analyzing the terminator's actions using the movie's logic, we can infer the reason behind its behaviour:
1. The terminator was damaged during the crash. We see in the next scene that its right arm is malfunctioning and that its left eyelid is permanently closed. It needs to repair its arm and remove said eyelid in order to see again. It goes to the police station only after repairing itself. We can assume it calculated that its chances to take down the officers (4 to 5 police cars with cops fully armed) were pretty low without the use of one arm and without depth perception.
2. It was running out of ammo. The terminator used a lot of ammo trying to take down Reese and Sarah in the chase. Later, when it repairs itself, it takes more weapons and ammo and goes to the police station.
We have seen in the movies that even if the T-800 is a walking tank, it is still vulnerable. If it had engaged in combat without full-combat capacity and with low ammo, and one of the cops decided to run it over with his police car once he saw the thing was a robot, it might have been taken down. When it attacks the police station, the terminator has the advantage, because the police aren't expecting a sudden attack into their headquarters. We see there is a lot of confusion and even having a building full of cops, only a few were able to hit it. Which leads us to another point:
3. The terminator is an infiltration unit. A thing that most people forgets is terminators aren't supposed to be demolition machines or assault troopers. Their first mission is to maintain a facade and keep it as long as possible to eliminate precise targets. We see that it does engage in full and open combat but only when there is a high chance to kill its target. Right after the crash, there were low chances to succeed, so the terminator fled from the scene. Even when it goes to the station, it first asks to see Sarah, trying to get to her in a way that doesn't draw too much attention. It is only after it can't get to her, and it knows she might be guarded by police for a long time (maybe even going to jail) that it takes the decision to assault the police station, and even then it does it in the quickest way possible. It doesn't go after each police officer. It cuts the lights off and tries to find and kill Sarah as fast as it can.