If you are out of luck, stranded with no vehicle, your next best option may be the train system. GTA 3 has a simple-to-use, always readily available, railway system that can take you all over the map. It is a completely free and super quick way to avoid traffic and get to where you need to go. Here is how to use it.
The L-Train
In a few specific locations, there are sets of stairs that will take you up to one of the platforms. From here you can climb up and wait for the train to come by. When the train stops at the station you can press whatever button you use to interact with to get on or off the train. For Xbox, this would be the Y button and for Playstation it would be the Triangle button.
Once you are on, the train will take you in a loop, stopping only at each station along the way. You can freely ride the train for as long as you want. In the image above, the train system is indicated by the dark red line. This is the path of the train. Following it by car or on foot will lead you to other staircases where you can get up to the station platform. The above loop travels around the east side of the map only. Other train lines are unlocked as you progress the main story.
For more Grand Theft Auto 3 - Definitive Edition guides, check out All Map Icons and what they mean in Grand Theft Auto 3 — Definitive Edition on Pro Game Guides!