Is It a Curve or Is It a Turn?

Making the turn, child in tow.

I've been looking at the intersection of 27th Street and Lombard Street in Philadelphia. It's a key part of the westbound access to the South Street bridge. The one thing I know for sure is that it is not an intersection. There is no westward extension of Lombard, past the intersection; and there is no 27th Street north of the intersection. 27th here is a one-block stub leading south to the bridge. There's another one-block stub of 27th just the other side of South, which feeds cars onto the bridge from Schuylkill Avenue.

Lombard and 27th are effectively one street that bends awkwardly at approximately 90 degrees, at the point where the nomenclature changes.

So this 90 degree thingy, is it a curve, or is it a turn? The people who designed and built this little stretch of road seem to have been genuinely conflicted by this question.

Lombard and 27th Street come together.

Here's another way of expressing the dilemma: Is it a city street, or is it an access ramp to the bridge and the Schuylkill Expressway, aka I-76?

Points in favor of ramp. There's no traffic light at Taney, the cross street just before 27th. (I think the ramp vibe starts at Taney.) There is also no traffic light at 27th, where there is, admittedly, no cross traffic. But the lack of a signal at these locations is a signal.

As you come to the turn, you'll notice the designers have gone to considerable effort to at least make it look like it's not a full 90 degree turn. The road widens substantially at the corner and the curbs don't form right angles, but instead present gentle, wide curves. On the inner side of the turn, this effect is enhanced by the judicious use of paint. All this encourages people to act as if they're swinging along on an interstate access ramp.

Finally, there are no crosswalks at Lombard and 27th. I personally think you'd have to be insane to try to walk across the street here, crosswalks or no crosswalks. But it's another little clue that this is not a city street.

(There are no crosswalks across Lombard at Taney either. People do walk across the street in this area with some regularity. Remember, there are lots and lots of people walking on the bridge, and they have to get there somehow.)

Points against ramp. If the turn at Lombard and 27th actually was an interstate access ramp, the curve would be banked.  A banked roadway makes it easier for cars to turn; it also means that all drainage goes to the low side of the bank, which in this case would be the left side of the road.

Instead, the street at this point has a crown in the middle and drains to both sides. This means that people on the right side of the road are turning on a surface that has reverse camber.  The problem with reverse camber in a turn is that it tends to throw you off the road. Which is why curves are generally banked.

Not surprisingly motorists tend to steer through this area slightly to the left of the crown, where the camber helps them turn. When they do this they need to avoid a large storm drain located in a depression in the pavement. They can do this by going to the right of the storm drain, or by straddling it. You don't want to put a wheel in that depression.

A storm drain for the motorists.

My friend Bill Marston thinks the drain probably started life next to the curb, but then the curb moved several feet closer to the building. If we accept this line of thinking, the streets engineers wasted their time moving the curb, because the bulk of the traffic is going to the right of the drain, and the motorists who are straddling could easily move to the right. So you have the appearance of a wider street, but not the reality. (The gap between the curb and the grate is 6' 6". I measured it.)

What's going on? I think the cartway's profile here is driven less by the needs of drivers and more by some thorny issues of drainage. The intersection of 27th and Lombard is at the bottom of two hills, one running down Lombard and the other coming down 27th from the bridge. When it rains, this intersection is definitely collecting storm water from a pretty wide area.

In addition to watching motorists, I've been watching bicyclists navigate through this area. They're hardly ever in the bike lane at the corner. They're to the left of it, I think for two main reasons: First, the higher route allows for a gentler curve. Second, there is a fearsome storm drain designed to catch the wheels of bicycles and eat them, and it's located at the curb in a particularly infelicitous spot. (I've also heard comments about gravel gathering in this spot. I wouldn't be surprised, since it's at the bottom of two hills. I just didn't see it.)

Storm drain in the bike lane.

I don't have solutions for any of these issues, but as we redo the bike lane in this section, I just wanted people to be aware of some of the design challenges.

Riding the curve.

See also Morning on Lombard Street, No Turn On Red, Put Traffic Lights on the Schuylkill Expressway.