Ray needs you to race him to the airport before the CIA can assassinate him. The lift bridge is heavily guarded so you'll need to take the tunnel.
Despite the warnings, it is possible although inadvisable to take the bridge. Your best bet is to hustle until you see the government agents in view and hop out of the car momentarily to take them out with a sniper or other strong weapon. They are heavily armed and are wearing armor so expect resistance.
Otherwise, the underground tunnel is more manageable. Three minutes is plenty of time to get to the airport gate, at which point Ray will give you the keys to his lockup. Head there and enjoy the rare bulletproof Patriot he left you.
$20,000 (+$20,000 in lockup)