Concrete patches in the slow lane

Yo Matt:

I have a question about some weird concrete patches in some of the slow lanes on our interstates. They’re rectangular cutouts, in two rows of four, very neatly patched. They seem to run right underneath cars’ tires. I have seen them in several places, like along westbound I-8 in La Mesa and a longer stretch on northbound I-5 as you enter San Clemente. But, again, there are these patches in several other sections as well. Are these patches covering up some sort of magnets to power experimental electrical cars along our freeways or was Jimmie Hoffa buried in thousands of tiny rectangles and covered in concrete along the interstates?

— Gotta Wonder, Clairemont

Hoffa? Preposterous! Everyone knows those patches are where CALTRANS buries pirate gold and blood diamonds to stockpile for the post-apocalyptic world in which municipal highway authorities rule the nation with an iron fist, dispensing justice as they see fit and fighting brutal turf wars over the right to command the interstates....

Oh, no, wait, those are patches over the spots where steel dowels were inserted to strengthen the concrete slabs that make up the roadway. It doesn’t show to the naked eye, but the huge slabs of concrete ripple and roll like waves as vehicles come along. The steel dowels are an inexpensive way to strengthen and prolong the life of the freeway by helping to transfer loads smoothly from one slab to another. As older roads are retrofitted, the bars are installed underneath the rightmost lanes because that’s where heavy trucks drive, hence the patches. Newer sections of freeway are being built with the dowels in place from the beginning.