First thing I noticed too.

Maybe the Freeways are there just for the Elite to travel on, and since this is the poor part of town there is no need for off ramps here. Everyday as they pass by the unwashed masses it would serve as the ultimate motivation to do well at work that day, lest they suffer the same tragic fate. Higher-up Government officials would pass over in their diplomatic transports and feel more secure that they were making the right decisions, because who among those apes down there could ever gather enough brain cells together to decide what was right for themselves? Children of the Elite would look down in wonder on their daily trips to the learning emporium, the mystery of it all would make the rumors they heard of beasts and chaos all the more terrifying and their teacher's refusal to answer questions on the subject would only make them more believable.

Meanwhile the poor unkempt average man would look up on his walk to work and imagine what it would be like to sit in the comfort of a transport as it whooshed it's way about the city, probably to some exotic restaurant or swanky club. His daydreams about the secrets these people must know and the adventures they went on would help him get through each hard, tedious day of labour. On his walk home to his family in a small, dirty, cramped apartment he would look up once more and think 'maybe one day...'

Or maybe the artist just thought the highways would look cool and doesn't have much experience with civil engineering.