Do own a copy of Midtown Madness 3? Do want to know all the good hiding spots and glitches? Then are you inluck. Here is a list of many secrets and glitches.
Click Here
First off click on this link to get a map of D.C.
(Click bottom right corner to make larger)
It'll help you know were to go and where the glithces are
K I do NOT know ANY glitches in Paris so sorry! (or else Ive forgotten them) 
Ok first off you can virtually get into ANY building anywhere. All you need is a small/medium CAR (lotus esprit works well) and a big truck (semi or fire truck). All you do is get a car against a wall.(In corners works best). Have the big truck ram the car and keep pushing until the car gets through the wall/fence. This is easier on xbox live, rather than splitscreen, because the game is trying to keep all players from lagging so the walls/barriers are easier to penetrate.
Train Yard glitch:
Single and 2-player
Go to Union Station. Its the yellow building on the edge of the map. There's also a metro station right by it.(By the Beetle RSI paint can) Drive down the road that's on the edge of the map that goes to Chinatown (Massachusetts Avenue). Drive down the street and go until you reach the part with the island in the road. Turn around and head towards the station.(This is so you can gain speed). Drive all the way down there and make the little curve S in the road(in front of the parking lot). Now you will need to hit the wall past the station. Its the one that turns and goes to the fence and into the yard. It has an orange and blue billboard and then goes to some buildings. This part is confusing, but you need to hit the wall at an angle(before the billboards)at a high enough speed that you will wall ride, hit the buildings, and fly into the yard. Once inside you can drive around quite a bit. Just be careful not to go back through the barrier. Yes this is confusing without video/pics, but if you're having trouble you can send me a fr and I can show you. The easier 2-player way is to go to the wall that you wall ride on and go to the the fence. Go to the corner thats on the right, the one that's where the fence meets the wall. (not the station meets the fence.) Have a big truck ram you and you should go through.
Secret Highway
Only 2-player
Go to the corner of the map by the island. Ok on the map there is a line for a highway. You've always wanted to get there right? Well here's how to do it. Go North to the part with the alleyways. It's the buildings to your right that has the escalade paint can and the skatepark. After the bridge over the channel there is a short brick wall to your right and a red building to your left. Take the 1st right into a courtyard. (there should be a statue at the end). Go into the right corner. Have a big truck push you in. Now once through there will be the secret highway to your right. but there will be a fall through between the solid that your on and the highway. Take a left and go all the way until you hit a solid wall. Turn around and go as fast as you can to hop the spot and land on the highway. Once on it you can drive all the way to the end and jump into the sea. The side barriers are passable so don't jump off the highway. You can still drive around on the grass, but you can't get back on the highway so you'll have to get through again. This is also confusing so good luck
Grassy Slopes of Georgtown:
Ok one is very difficult so don't get discouraged for it is tough to do. Go to the Circle where you find the D.C. Police spray can. Now go down Massachusetts Avenue a ways (East). Then turn around and pick up speed. Go under the circle and keep accelerating. As you come out of the tunnel watch the island in the middle of the road. Now at the end of the road you'll see the road turning left with houses to your right. When your going at the top speed you must ram into the wall/invisible barrier. You have to hit around the 1st dark blue house. Now here's the hard part. You will wall ride until you go over the invisible wall. Now you can't brake before you hit the wall or you'll lose speed and not wallride. But while flying through the air you must brake. Reason being is because your trying to get on the slopes behind the houses that is next to the Rock Creek and Potamic Parkway. In the air you must brake so as you aren't going top speed and fall back onto the road. But you can't brake to soon or you'll go throught the houses and respawn back onto the street. You have to get it just right so as you land on the grassy hill. If you do you can explore. Don't fall back onto the road though. You can drive through the 3 houses and all along the back of the map. You'll notice on the North end that there's a river with another slope on the other side. Sadly the other hill isn't solid
. You can fly into the water as much as you want but there is a catch. If you slowly fall down the hill and go into the water close to the hill you will keep respawing by falling into the river. You will have no choice but to reset your car and get out again. Once again this is a hard glitch and takes alot of practice.
Parking Structure Glitch:
Go to D.C. and go to the parking structure in China Town (not in Georgetown). Go to the top level. Now you'll see another level on top of that that you can't get to and the roof. Go to the opposite side you came up and go to the edge. Now here's the tricky part. You need to "glitch out" your car. You can do this by putting your car in the corner next to the pole or falling down on the ramp and landing on the top of your car. Sometimes the game instead of spawning you back a couple feet it will spawn you on top of the parking structure! An even easier way to do this is put your car in the spot, and then on a hunter game have a police car hit you. You will become the police and will most likely spawn ontop of the p.s. You can drive around and your wheels will be hovering about 3 feet off the roof.
Small Roof Glitch:
Get a fast car. Go to the parking structure in Chinatown. You'll notice that there is a big building on the same lot, with a bunch of construction stuff in between. Facing that building with the p.s. behind you go to the right. You'll see right by the street on the building a small awning roof. Go down the street that runs all the way down to the mall. Turn around and head to the p.s. You'll come to the lot and the awning will be almost straight in front of you. Ram the red office things that are stationary and you'll go straight up in the air. You want to aim a little to the right so you can land on the awning!
China Town Roof:
This one's simple. Get a semi fast car. Go to china town and go the courtyard with the alley behind it. Go all the way down that till you hit the building. Turn around go down the street then down the alley. Go up the ramp and you can land on the roof tops!
Freak Accident:
Ok this is similiar to the p.s. glitch. I was playing a hunter game at the mall. I wasn't it and was hiding from the police in the building with the underground parking lot (below the building). Anyway a police car came in and tagged me. I became a p.c. but spawned on top of the building! 
Georgetown Park:
When your on the back highway at Georgetown you always see the park across the river right? Well sadly you cannot go over there. I have tried to get over there many ways including jumping across the river only to hit an invisible barrier. I have also tried getting through the walls on the other side, but the ground is not solid. You sink right through. Sadly you cannot get there. 
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