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 of running down a hallway on Space Colony 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 robots, as well as a few lightning fast (and dangerous) bomber jets.
This section requires an expansion.
Level Up Item
Shadow's Flame Ring Level Up Item is found here. He needs the Air Shoes to obtain it easily, but he can also reach it without them by using a Spin Dash and jumping across a gap at the right moment.
Collect 100 Rings
If the player stays in the middle of the road where most of the Rings are, this mission can be completed quickly. If the player has the Air Shoes to Light Speed Dash, this mission can be completed even more easily.
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. They must gather speed and perform a trick on it. This panel provides a fast shortcut to a Spring overhead, which will launch the player to a platform above with a horizontal pole at the end of it. They must swing upon the pole to fly to the elevators.
The player must 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, they should grind down either one of the cables on the left or the right which is 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 thus take the high route, where the series of enemies has been replaced by a single enemy followed by a path of Rings. They must 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 are now only accessible if the player attacks the Gold Beetle at the right time.
Chao Container locations
The first Chao Container is tucked in a small nook to the left of the stack of Wooden Containers and the first Pulley in the stage.
After the first Point Marker, the second Chao Container is on a ledge just below the series of Gun Beetles the player can Homing Attack across.
After the second Point Marker, the player can see the third Chao Container tucked among Wooden Containers just after the bridge section.
Radical Highway is based off of 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". Additionally, on a sign on the other side of it, it says "Freedom ? miles", which most likely alludes to the dark story.
In Sonic Generations on the Nintendo 3DS, 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.