One advantage associated with driving on side streets is drivers more likely to be attentive lighter traffic during rush hours multiple lanes of traffic in each direction

The answer is - Lighter traffic through rush hours.

The traffic during rush hours is terrible, especially in the big cities, when millions of vehicles are on the streets and everything is blocked and slowed down, which understandably no one likes. 
When driving on the side streets though, the traffic in the bigger streets becomes much more bearable and is much faster, so both the drivers that use the side streets benefit from being quicker and evading big traffic, and the ones that drive through the bigger venues have it easier because there's much less traffic and everything is sped up.

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