Radical Highway is Shadow's first stage on the Dark Story in Sonic Adventure 2. This level takes place in an area that resembles San Francisco's Golden Gate Bridge (in the dead of night), which further enhances the "Central City" atmosphere.
Shadow is surrounded by the military and police after stealing the Chaos Emerald from the federal reserve bank. As he watches them, he has a flashback a running down a hallway on the ARK with Maria. Returning back to the present, Shadow promises Maria revenge against humans.
Throughout the stage, there are huge suspension cables of the bridge that Shadow can grind on. Performing tricks perfectly will get you far in this level, as they can allow you to cover great distances and skip large sections. This level has many enemy bots, as well as a few lightning fast (and dangerous) bomber jets.
Collect 100 Rings
If the player stays in the middle of the road where most of the Rings are, speedy completion of this mission should be a breeze. If the player has the Air Shoes to Light Speed Dash, this mission can be completed easier.
Find the Lost Chao
Getting to the necessary Ancient Ruin for this mission can be a little tricky. After the second Point Marker and after the second screw loop, the player should see a Trick Jump Panel ahead of them. Gather enough speed and perform a trick on it. This panel provides a fast shortcut to a Spring overhead. This Spring will launch the player to a platform above with a horizontal pole at the end of it. Swing upon the pole to fly to the elevators. Reach the top platform, and Homing Attack across the Spark Beetles ahead to access the platform that leads to one of the bridge's support towers. From that point, grind down either one of the cables on the left or the right cable at the tower that positioned behind the player to reach the previous support tower. On that tower is the Ancient Ruin, which when activated, will make a pair of platforms appear. These platforms lead to another platform where the lost Chao is.
Reach the Goal within 3:00
This mission is extremely difficult and requires mastery over this stage to complete it. Light Speed Dash whenever possible, launch from every Trick Jump Panel, and swing from every horizontal pole.
Clear Hard Mode
In Hard Mode, it is more difficult to get across the bottomless pits. The safety net is also gone. The player must therefore take the high route, where the series of enemies has been replaced by a single enemy followed by a path of Rings. Hit this enemy with the Homing Attack and then Light Speed Dash along the string of Rings to get to the other side.
The elevators that come after the bridge section is now only accessible if the player attacks the Gold Beetle at the right time.
Big the Cat sighting
Big the Cat can be seen on the wing of a blimp in this stage after the second rocket ride (third if counting the rocket on the Flame Ring's road).
Radical Highway (or somewhere similar) is where the opening cut-scene took place in Sonic Adventure 2.
A remixed version of the Radical Highway theme appears in the 2P battle mode of Shadow the Hedgehog.
Radical Highway is based off San Francisco's Golden Gate Bridge along with other stages.
By looking at the "Caution!" signs scattered around the level, it's safe to assume that parts of Radical Highway were under construction when Shadow was running through it.
NiGHTS' head can be seen spinning on top of a building.
There are highway signs in this level saying "Amigo" in this level, also on a sign on the other side of it, it says "Freedom ? miles", which most likely alludes to the dark story.
In Sonic Generations, the player plays as Sonic the Hedgehog instead of Shadow. However, Shadow is still present in Radical Highway, as the rival battle takes place there.
The Mario & Sonic incarnation of Radical Highway is the only one to have a different blimp to the others, as the one from Mario & Sonic literally says "Radical Highway" instead of "Got Ring?" or the Soap logo. The NiGHTS cameos are also removed, most likely to keep the represented series to just Mario and Sonic.
There is a sign that reads" Time Eater" who is the main villain in the game Sonic Generations. The sign only appears in the Sonic Generations version of the stage.