Hold onto your hubcaps.

The city's Department of Public Works is projecting rougher riding ahead for the next few years on the city's residential streets. It's projecting that the pavement condition index (PCI) for residential streets will slide from the current level of 70 on a scale of 100 to 68 by 2016. Although a two-point drop may not be noticeable for the typical motorist, the drop since the 83 points recorded in 2000 may be more rattling.

The projected drop also means that by 2015, the city's residential streets could be in worse shape than its commercial streets, barring a stepped-up residential paving program. That would reverse a long-term pattern since the city finished its residential paving program in the 1990s.

The city made a concentrated effort under Mayor R.T. Rybak to concentrate street improvement dollars on major streets like Nicollet, Riverside and Central avenues. The reasoning was that those carry a much greater proportion of traffic than side streets, so the city would get more bang for the buck. But that investment raised the PCI for those state-aid streets by a mere four points, from a rating of 66 in 2010 to 70 in 2013. Now the department is projecting that at planned capital spending rates, the PCI will drop by a point next year, before returning to the current level for the following two years.

Part of the city's reasoning for not paying as much attention to the streets where people live is that the residential system generally was paved more recently than many major streets. But the projected slip of the residential system below the state-aid arterials suggests that thinking may be out of date. The department's web site lists seven potential residential paving projects this year.

The pavement condition index represents an effort by city workers to rate the surface condition of city streets, but doesn't address underlying conditions that may be contributing to the need to patch them frequently. The city switched strategies in the last several years toward milling away the surface of streets that are not too far gone, then repaving them with a new layer of asphalt. That doesn't last as long as a complete reconstruction but it allows the city to finish more miles of streets.

(The section of Nicollet Avenue shown above was one of the worst in the city until it was reconstructed in 2013 as one of the city's commercial street renovations.)