On any city street you are likely to see delivery vans, couriers, salespeople, and utility persons making frequent stops as they conduct their business. Some people spend many hours in traffic just going to and from work. Even though the mileage may be small, the amount of time spent on the road is very long. Every hour spent on the road increases your chance of having an accident. Certainly speed is a factor in accidents.
Many accidents happen simply because the driver is going too fast.
City streets usually have speed limits of less than 25 miles per hour, and often you will see posted limits as low as 5 or 10 miles per hour. Speed limits are carefully selected to minimize the chances of accidents. When traffic is heavy, there just isn't very much distance between you and the next vehicle to stop. The slower you're going, the less distance it will take to stop. By going slowly, you will also be able to observe your surroundings more easily, taking note of cyclists, pedestrians, and other vehicles.