My question (to get to the meat of it) is whether there is a disparity in speed at which you find it unsafe to ride.

Does the availability of a shoulder make a difference? Distance ridden along that road?

Yes: This comes from a new cyclist who lacks confidence and likely just needs to HTFU. But I'm still curious.

I've been looking at routes online to go some places, hoping to find an alternative to a four-lane divided highway (numbered US highway, not Interstate) with a 55 to 65 miles-per-hour speed limit (55 in town 65 outside of town), typically driven at 70+ (and the not so uncommon 90+mph driver). There's often a shoulder, with ruble strips. At least in those areas I'd have a way safely out of traffic.

But many local roads, mostly with speed limits 45-55mph (driven 65+ most of the time) there are no shoulders (a few inches of gravel then sloping grass or a ditch), and lost of somewhat blind curves, and frequently appreciable hills -- especially to a n00b like me who also still has a crap bike (I wish saving for a decent ride were easier!).

I add to this a local culture of angry and aggressive drivers. In my car, I am almost rear-ended nearly every morning in the early part of my commute to work by someone who wants to drive faster than I'm moving, and ignores turn signals.

I've seen another cyclist on the road -- once a long time ago -- and didn't think about asking him. Most people -- even the very serious (looking) folks -- drive their bikes to the local MUP in stead of riding there. Granted, I don't know the distance they have to get there, or other possible factors leading to their decision to do so.

But the MUP is just a few hilly miles away, not too far from there are some places I frequent, and in the opposite direction from home are the others. When I'm in better shape (hills still do me in after a whole three weeks lol), I'd prefer to leave the car at home more often.

Riding a bike is never 100% risk free. The degree of risk varies with the circumstances. Deciding whether it's safe enough or not is a matter of personal assessment of the degree of risk and risk tolerance. The speed of the traffic is just one factor in my personal assessment of risk. The road situation and traffic density figure in more strongly. I've ridden on interstates with traffic passing at 75 mph in a few places where it's legal (and maybe a few where it wasn't) and felt fine. I've been in situations where traffic was very dense moving ~30mph on 6 lane roads with lanes merging on and off the road and felt it was much more sketchy.

Sounds like good 'ol autocentric designing, and the engineer's quest to increase traffic movement efficiency, along with the focusing on the group of road users that garner the highest number of commute minutes and being able to stick a feather in their cap when a large number of commute minutes is easily reduced due to overall speed increases, which usually comes at the expense of other road users, non motorized especially.

Sounds like you live in an unfortunately car-centric location!

As to your original question: Yes, wide shoulders help. The main highway near me (the Trans-Canada) has a huge shoulder, and it feels pretty safe to ride on it. However, I tend to prefer less-travelled roads because of the noise. The sound of people passing you at highway speeds really starts to wear on you after a while.

If I have the choice between a low-volume narrow-shouldered road and a high-volume wide-shouldered road, I'd take the low-volume for long distances (touring) and the high-volume for shorter more aggressive training rides.

In my experience, the relative safety of various roads isn't so much a matter of construction, traffic density, or speed, as it is one of driver expectations. If you're riding on roads often used by cyclists, drivers will (by and large) be more alert and see you sooner than a road where they don't expect to see anything other than cas moving at the same speed as you.

In this context bad pavement areas, turning traffic, children playing, parked cars and trucks, and other obstructions become your friends because they raise driver alertness and focus on their driving. As a rule, people see what they expect to see, and don't register stuff (like you on a bike) that they don't as quickly.

Other than expectations, you have to use your own judgement about other factors. Neighborhood streets are safer than main highways, multi-lane can work for you by giving cars a lane to move to, and against you if traffic is heavier, by making drivers nervous about moving to the adjacent lane, concrete roads, and those where the shoulder is detached from traffic lanes pose a unique risk because the burm itself can cause you to lose control as you cross it (do not cross back onto the main lanes over a burm except at a sharp angle, as you would if crossing RR tracks).

Probably the most important safety factor is your ability to ride in a straight line, and hold line as traffic passes. I've witnessed accidents where a cyclists swerve on being passed by one car brings them into the path of a following car, so steel nerves are definitely the order of the day when sharing roads.

+1. That's my experience. No matter how many cars honk at me, I am not giving up my position unless my life depends on it or an emergency vehicle is passing. I will not sacrifice my saftey and right to use the road for a driver's convenience. THEY can slow down for 10 seconds and pass when it is SAFE to do so, not demand that I get out of their way.

For me, a shoulder doesn't make difference. Because, While they are good for bikes, they are also a green light, for the motorists' to drive as fast they want to.

What area do you live in, that puts you directly in the midst of high-speed traffic?

How local are you referring to? By that I mean, are they a block away, or outside your front door? Where I live, most the cities n' towns in the metro region have 30-45mph speed limits. Once you get beyond suburbia, in to the country, the speed limits increase to 50-55mph

That is a given, anywhere. Something happens to a person, when they get behind the wheel.

This has baffled me for a long time. I go 25mi. on my bike just for a 16mi. club ride. I don't ride anything else to get there.

Good

I suspect that it depends more on driver and cyclist culture than anything else.

In the UK, it's still common for time trials to take place on dual carriageways with 70mph limit - in part because the speed of passing traffic increases the speed at which a rider travels. I've done it with no particular anxiety, except at the traditional roundabout turn when having to go from first lane to third to get onto roundabout in the appropriate place.

Before I retired, my daily commuting route required something similar, except that, during the rush hour the trraffic was going more slowly than the 70 limit, so I always managed the manoeuvre (over two lanes, not three) - not always without trepidation, but there would always be drivers willing to slow down rather more in advance of the roundabout than they would normally do. Whether I'd have been able to do that in the US with the same level of safety may be another matter entirely

Thanks for the replies, everyone. Perhaps I should have been a touch more clear, saying that I wouldn't ride on the shoulder (when there is one), but that it would be a means of escape if things get desperate.

And yes: The area is not designed for any vehicles besides those with an engine and two or more tires (I'd have said four, but that would leave out motorcycles )

It's rural Georgia. The area roads are basically this way: One US highway, four lanes divided, 45 in-town speed limit, 55mph limit until the north/west end of this town, when the speed limit posts at 65mph. If I want to go anywhere north or west, that one highway is my only option; I could leave the road and bypass in neighborhoods along the way, but not even for a mile at a time once I'm out of town. Another highway leads a bit more east (the one where my neighborhood is located), and the two are connected by several side roads and some county roads.

Local as in just at the exit of the neighborhood, and generally a five-mile radius of roads to access most of the places I frequent here (groceries, the closest movie theater in 30 minutes, etc.). Here are the left and right views from the end of the neighborhood. The right view is fairly OK, but drivers coming from the left are frequently driving 55mph or faster, making turns into traffic a serious risk even in a car.

(right)


(left)


Some rough maps and street-view screen captures:

This is one of the roads I will take on a longer journey. The speed limit is 55mph, and I'm tailgated every time I drive through.


This is an example of the four-lane divided highway outside of town. Besides merges from the right and the occasional intersection with a traffic signal, this is basically what the majority of the ride outside of town will be like.


As far as closer to home, the things in one direction are somewhat conveniently accessible from back roads and the MUP, and there's also a road paralleling the main highway within the shopping center. My concern is more the roads between home and the destination. My current plan is to get a bicycle I can add fenders and racks to, for local trips (and some longer rides as well, down the Silver Comet Trail, perhaps Chief Ladiga before too incredibly long), while I decide what my then +1 will be. My current POS will either be donated to a bike charity back in Atlanta, the thrift store, or something else worthy of a Huffy.

At least uncomfortable, sure. The further above 40mph it gets, the more uncomfortable I am. I haven't encountered a road with such disparity that I refused to ride it, but that brings me to...

Yes, on both counts. There is a 50-55mph road I ride on for a few miles that doesn't bother me at all because it is insanely wide with insanely wide shoulders. Tons of room between me and drivers. If there were no shoulder or an unridable/small shoulder, I might think twice. Basically, for me, as a rule of thumb, the greater the speed disparity the greater room for passing is needed. If I only have to ride on a "crappy" road for not very long, it doesn't bother me too much.

I ride and commute because I like to and it is a fun way to get some exercise, fresh air, and destress. If I had to ride in conditions that stressed me out, it would defeat the purpose for me. Others may be different.

If you wear a helmet or glasses, I'd recommend either a glasses or helmet mounted mirror to help monitor approaching traffic in the kind of roads you are talking about. Does a lot to set your mind at ease, and I believe helps ensure safer passes as you can move right more if needed. How much they help is very debatable, as the active threads on that subject will show .

Best of luck with whatever you end up doing.

I can see that, especially in the U.S 278 photo where the barely usable shoulder would be bad in itself, but the addition of rumble strips down the center of it sealed the deal.

As others have noted, the question is not purely speed, but depends more sight lines, law enforcement, and driver behavior (typically depends on laws actually enforced).

Locally (DE/PA border) the roads with 45-55mph speed limits will be built with better sight lines for motorist safety, and frequently have multiple lanes and/or shoulders. With good sight lines and multiple lanes, I haven't had serious problems with 40-50 mph speed limits (traffic usually 45-65mph). Also in these areas, if traffic is light there will be anywhere from 2-4 lanes available for passing and motorists just use the extra lanes. If it is congested speed falls to 20-40 mph.

In other parts of DE and PA there are more roads with no shoulders and poor sight lines, but some motorists will still exceed speed limits and sight lines. I have used these roads on occasion without problem, but I will often use the major highways since they have good sight lines and passing lanes. When I've driven on some of the smaller (no shoulder roads) I tend to go the speed limit, but I've seen enough deer bodies near the road to convince me that others are too impatient to drive safely. (My understanding is that hitting deer will total many cars. Since I've been able to avoid many deer by driving close to or below the speed limit, I assume the bodies are proof some one else was driving too fast.)

To spell this out, I feel safer with traffic at actual 45-60 on roads with multiple lanes/shoulders than I do at 40-45 with no shoulder or sightline. In your situation, I would look at sight lines, and police driver attitudes. Do motorists in GA leave reasonable passing distance, or do they throw bottles at bicyclists? Do the police believe bicyclists are allowed to use the roads, or will they automatically fault the bicyclist in any collision? (I haven't been cited, but I've been pulled over twice when riding legally by police that had severely limited understanding of the traffic code.)

This is something I have no idea about in this area, as far as interactions with cyclists. Often, people driving far above the speed limit here aren't capable of responsibly operating the vehicle at that speed (I'm a bit of the reckless type who thinks it's fine to speed when safe to do so ... I know, a can of worms here but not tailgating, being patient for slower traffic, etc. falls into that), and being able to correctly judge the vehicle's capabilities for a curvy road is part of that, and so is holding the lane.

And as you cited with lines of sight, that's one of my larger concerns; As with the curving road just outside the neighborhood, there are also some other curves and hills over and around which it is difficult to see. I've approached tall trucks over some local hills, being able to see far ahead of the crest but not just beyond, having no idea they were there or had just turned into the road space. That's one of the reasons I refuse to speed on those roads. But having been nearly rammed by people flying through, it causes some trepidation for the potential of riding a bicycle on those same hills.

Sometimes I really miss some aspects of living in Midtown Atlanta -- except I've seen my fair share of motorists doing stupid things, and stupid things to cyclists, there. The grass is greener, you know.

I have a recent post on this subject HERE. In brief:
The online & downloadable NHTSA FARS data for 2009 data show the following for the posted speed limit where fatal bicyclist-motorvehicle crashes occurred (I graphed this before the 2010 FARS with the PBCAT data was available):

For those unfamiliar with cumulative quantile plots such as above, the y-axis is the cumulative percent of dead bicyclists at or below the posted speed limit on the x-axis. Each point on the graph represents one dead cyclist. With hundreds of dead cyclists/year, each dot is quite small and they then merge to form a "line", but if the original graph is viewed at enough magnification you can see the individual data points.

Reading the quantile plot shows, for example, that only about 20% of fatal crashes are on roads with speed limit of 30 mph or less. Not surprisingly, higher speeds are associated with most of the fatalities. My estimate is more that 20% of bicyclist exposure (time or distance traveled) is on roads with posted speed limits of 30 mph or less, so the fact that only 20% of fatalities were on such roads indicates they are safer.