After pressing start, you'll be thrown onto a highway. As you make your way right, you'll notice cars driving past - some of them in pretty bad condition. Immediately after, you'll face your first enemy: a rolling spiked wheel.
After the wheel, there's a missile guy. Jump the gap, then get ready to face several flying enemies that carry spikes underneath. When you destroy them, they drop the spikes. If the spikes land on a part of the highway that is vulnerable, it will destroy it. You'll notice that if enough of the highway breaks away, a gap can be created. Also notice that the only breakable parts are between the poles that support the highway. The sprites for those sections (they are square and sometimes have a street lamp on them) are invulnerable so if you time your kills correctly you won't have to worry about falling or jumping around uneven terrain.