Rescue Vehicles

Throughout Left 4 Dead, there are four rescue vehicles, each appearing during the finale of any campaign. The goal of the Survivors is to reach these vehicles, which will take them to a point that is safe from the Infection. Each vehicle is summoned via some type of radio, and each vehicle takes approximately ten to fifteen minutes to arrive at the Survivors' position. In the mean time, the Survivors are kept busy with multiple waves of the Infected.

Rooftop Finale
Through the city of Fairfield, a helicopter called News Chopper 5 flies through the skies, calling out to any Survivors left in the city. The pilot tells anybody who can hear him to get to Mercy Hospital, where he can pick them up. At the end of the No Mercy campaign, the Survivors reach the roof of Mercy Hospital and find a radio to summon their rescue with. During their wait for the helicopter, the pilot mentions that this will probably be his last trip--a remnant of another ending to the campaign.

The Truck Depot Finale
After News Chopper Five crashes in a small fishing town just behind Riverside, the survivors attempt to walk to Riverside. They stumble upon an armored mail truck on a lift in a truck garage. The lift is powered to lower the truck, which the survivors ride out of the town to Riverside.

Boathouse Finale
Outside of the small town of Riverside is a boathouse. On a table inside is a radio, being hailed by John and Amanda Slater, who own the S.S. Saint Lidia II, a small fishing vessel. It has been circling around the river while John attempts to hail anybody who had survived the Infection, offering to take any armed survivors to a military holdout up the river. Fortunately, there are plenty of weapons to supply people with. At the end of the Death Toll campaign, the Survivors find the boathouse and answer the radio, making use of the various firearms around the building to help them wait through the hordes.

Runway Finale
At the beginning of the Dead Air campaign, a military C-130 Hercules plane flies over the city of Newburg, heading to the Metro International Airport. It finds the airport has been obliterated under the Infection, and any personnel that would otherwise be able to help the pilot have been killed or Infected. It may be that there were still a few left alive because when the Survivors get there, the fuel line is already connected. However, the Survivors reach the airport at the end of the campaign to find the plane. They answer a radio which is in the hands of a corpse next to a gas pump and agree to help the pilot, as they are otherwise stranded. They start the pump, and wait through waves of the Infected for the tank to fill.

Farmhouse Finale
In a rural area, the army had locked down a farm to help Survivors escape the Infection. At least, until they themselves were forced to leave. However, they did not give up all hope on anybody surviving; they left a radio behind. At the end of the Blood Harvest campaign, the Survivors reach the farmhouse where the radio is, and call for their rescue, then hold off the horde while waiting for the army to arrive. In the end they are taken to safety by a Sisu Pasi. 

The Table Bridge
The complete abandonment of the mainland forced the army to bring rescued survivors out to sea, as the Infected can't swim very well...yet. Now, after the evacuations have stopped, the four Survivors need to get out of the proverbial dodge as soon as they possibly can, if they want to survive. Ultimately, the Survivors are rescued by a military CH-53E Super Stallion, which flies them to the cruise ship.

The Plantation
In The Plantation, the Survivors hold out Left 4 Dead style, until a boat appears. The boat currently has the model of the Death Toll boat, most likely as a placeholder.

Trivia

 * Originally, Valve had the idea of News Chopper 5 ' s pilot asking for a first aid kit, saying that he wasn't feeling well after he made an attempt to rescue some Survivors from the street, which he knew was a dangerous move. Shortly thereafter, the pilot would state he was very cold, begin coughing, turn and become infected, more than likely from wounds caused during his street pickup, and the helicopter would crash, beginning the Death Toll campaign. However, they felt that this would be an unsatisfactory ending to the campaign, and cut it out, though they leave the preceding dialogue in the final version. Proof of this can be found on the Youtube video here. This ending seems to have been restored with the Crash Course campaign.
 * There is a large poster advertising the News Chopper 5 at the start of The Subway. It can be seen as the Survivors go down the stairs and into the first station's ticket booth area.
 * The C-130 at the end of the Dead Air campaign is (somewhat erroneously) modeled after a South Korean Air Force C-130, rather than a U.S. Air Force aircraft. In game shot Real life reference . Note the identical markings (ROKAF 55, 036) and the identical camouflage paint job.
 * The license plate of the vehicle at the farmhouse finale is the same number as the stormtrooper uniform (TK-421) Luke Skywalker wears in Star Wars Episode IV: A New Hope.
 * If a Survivor or Infected dies in a rescue vehicle, their body and equipment will float in the air while the rescue vehicle moves away.