After Shadow destroys the Black Arms in the city, he continues on to a long stretch of highway. Black Doom decides to get out of town after acquiring a third Chaos Emerald (perhaps due to Shadow and Sonic's total xenocide in downtown Westopolis), demanding that Shadow accompanies him with the other two emeralds thus collected. Sonic, however, needs help destroying the Black Arms' lead tank. Either way, at the end of the level Shadow demands that Doom surrenders the yellow Emerald to him. Unimpressed, Doom summons Black Bull to charbroil Westopolis and Shadow. If you obediently followed Black Doom, after defeating the boss Shadow will warp to the next stop in his whirlwind adventure, Prison Island. If you destroyed Doom's precious Black Tank, however, Shadow will then wander about for the fourth Chaos Emerald before stumbling upon Circus Park.
The following weapons can be found in Lethal Highway:
Run down the highway after Checkpoint 1 as fast as you can, and get by the bomb before it explodes, so you stay on the top level. The key is shortly after that.
Use the Chaos Blast in the room just after Checkpoint 2 to destroy the nearly indestructible substance.
After coming out of the first room just beyond Checkpoint 2, a piece of the highway will fall, and the Black Tank will fly across. Go back to where the tank came from to get the key underneath the car.
Following Checkpoint 3, you will get to a point with a chain link fence and two dash panels. Use the dash panels to bridge the gap. Turn around and drop straight off the edge for the key.
After grinding the red vine, you will see the Black Tank materialize. Go behind where it came from, and destroy the broken down car to find the key.
Destroy the Black Arms' tank before it reaches the end of the stage.
Shooting the tank will not do any good at first, but after being shot sufficiently, the tank's barrier will be destroyed. Rapid fire guns are very helpful with this part. Once the barrier is destroyed, the tank can then be destroyed with just one Homing Attack or just one gun shot. If the aliens managed to escape before Shadow destroys the tank, restart from the last checkpoint (the point where the aliens haven't escaped). However, an A-Rank is unobtainable using this method. If no save points are touched and the stage is restarted before the tank gets away, the tank will still have taken damage. Be sure to fire all you have at the tank, and when lacking a gun, homing attack it.
If the player has beaten the game and has unlocked the Shadow Rifle, the player can deal massive amounts of damage to the shield. Only after about 6 hits, the shield will fall. This also gives an A-Rank.
Tips: Its eye is the weak point. You can attack when he bends down to attack you or when he releases the birds. If you're ever low on rings, there are 5 ring item boxes in some of the corners of the stage. When Black Bull is at half health, Black Arms soldiers armed with weapons will appear on the path. You can steal a gun from the Black Arms and try use it against Black Bull, but he'll flee the moment you fire at him. If you use Chaos Control, Black Bull will have virtually no chance of escaping, allowing for an easy kill.
Behind the Secret Door
Two handheld G.U.N. mech Gatling turrets. These are usually used to aid in the Hero Mission (destroying the craft).
The name of this stage, 'Lethal Highway', is a reference to the Sonic Adventure 2 level 'Radical Highway'.
There is no checkpoint at the end of the stage.
This is one of the few stages in the game to not have a Neutral mission.
During the stage there are billboards showing NiGHTS flying.
This is the only level to feature the original Dark Rider.
This level is the only time Sonic officially swears. If the player fails to destroy the Black Arms' Tank, the "HERO MISSION FAILED" icon will appear and Sonic will say "Damn, they got away! Leave it to me, I'll chase them down."
In the cutscene before the stage, Sonic will say "Welcome to the next level", This could possibly be a fourth wall break. Of course, Sonic was probably just making a joke.
It is also a reference to one of the slogans used for the Sega Genesis, where Sonic made his debut.
Chunks of road falling on the path can be interacted with before they fall if the player is fast enough.