Slow by nature

Although the vast majority of vehicles are driven at the “normal speed of traffic” — there are many classes of vehicle (or device) which are by their nature sometimes or always driven at less than the normal speed of traffic, yet are generally allowed on the roadway. These include both motorized and non-motorized vehicles. Operation of these vehicles/devices is allowed unless specifically prohibited; for example bicyclists and motor-driven cycles are not permitted in the roadway on limited access highways. They can also be prohibited by minimum speed limits, however as noted here, in Arizona “Posted minimum speeds are rare. There are NO KNOWN posted minimums on any street in Arizona”.

Besides bicycles, there are many classes of vehicle permitted on any street in Arizona with limitations as noted, these are just examples, there are probably others:

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  Motor driven cycles: (like a motorcycle but with < 5hp engine. Often called motor scooters). These vehicles are designed to operate at approx 35mph maximum; although because of the limited amount of power, variations in rider’s weight. wind, and grade can significantly slow them.
  Though they are prohibited from limited access highways; they will often be operated on streets well below the posted maximum speed limit and slower than the normal speed of traffic. Here’s a great youtube from Honda instructing motor-scooter drivers to NOT hug the right edge; the text is in Portuguese, but the concepts are apparent and identical to advice for bicyclists.

• Animal Riders, and Drivers of animal drawn vehicles; speed varies from very slow to at most moderate, though in any case well below any maximum speed limit and slower than the normal speed of traffic.
• Motorized Farm equipment / vehicles
• Mopeds; by design can go no faster than 25mph. And incidentally mopeds aren’t allowed in bike lanes, they must ride in general travel lanes, you know, with the cars.
• Motorized bicycles; are permitted to only be operated below 20mph
• Heavy Trucks; frequently (e.g. due to the up to 80,000 pound loads, or grades) will be traveling below posted maximums and slower than the normal speed of traffic for extended periods. I routinely travel at the same speed on my bicycle as heavy trucks for 1.5 miles on 45mph limit roads.

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  Construction Equipment moving ‘incidentally’ on the road; backhoes, etc. Typically can travel no faster than ~ 20mph. I pass various tractors and bobcats on my bike going quite a bit slower than that.

• Other motor vehicles moved only ‘incidentally’ on the highway: e.g. Landscape equipment / riding lawn mowers / atv, etc can frequently be driven only significantly below posted maximums.
• Low Speed Vehicles (a.k.a. golf carts, Neighborhood Electric Vehicles) designed and operated at a maximum speed of 25mph. These vehicles are permitted on any street in Arizona with speed limits below 40mph — as such will be traveling well below the speed limit on 30 and 35mph posted roads, and also slower than the normal speed of traffic.
• (city transit) Buses; frequently drive below posted maximums. To give you some idea of how slow, the bus I ride on is timed to make 15mph, it runs along a 45mph posted arterial road. They of course periodically completely stop, completely blocking a lane of traffic for as much as several minutes at a time.
  School Buses: when passengers are loading/unloading all traffic in all lanes in all directions must stop, what’s that, super-impeding?
• Street sweepers in operation travel at about 15mph; I regularly pass them — that is if it’s safe, and I choose to do so; if not I will be impeded by them.
• Bicycles will be operated at any speed from very slowly on up. They will typically be operated well below the maximum posted speed limit, as well as slower than the normal speed of traffic. Bicycles are permitted on any street in Arizona with the exception of in the roadway of limited-access highways.

These road users are sometimes going to be going slower than the “normal speed of traffic”. This is by design, and is the expected use of these roads.

These are all types of traffic which sometimes or even always operate significantly below the posted maximum speed limit, or “slower than the normal speed of traffic”  — both motorized and non-motorized that are both permitted and expected users of all roads; with the exception of limited-access highways.

Note that all these examples cited above are  by definition traffic:

§28-601,  28 “Traffic” means pedestrians, ridden or herded animals, vehicles and other conveyances either singly or together while using a highway for purposes of travel.

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Arizona Drivers Manual

P. 42 Arizona Drivers License Manual (emphasis added):

Slow Moving Vehicles
Farm machinery and other slow-moving vehicles can be particularly hazardous. Be sure to maintain a safe following distance that provides an adequate field of vision.
Farm machinery usually travels at 25 mph or less, may take up more than one lane of the road, and may not have signals…
Do not become impatient if you find yourself behind one of these slow vehicles. It has the legal right to be there.

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There are a number of examples of warning signage about slow moving vehicles using the highway in Motoring vs Bicycling Signs and Markings ; “Be Alert for Slow Moving or Stopped Trucks”; “Slow Moving School Buses Use This Highway Next 20 Miles” (I-40 in NC) — this must be a common occurrence if they put up a sign; are the drivers of these trucks and buses in violation?

Impeding?

So, if these vehicles are impeding, or even just potentially impeding other traffic, isn’t that illegal? No, of course not. There is no published Arizona case law on this point, probably because it is self-evident that simply traveling slowly can’t be considered a violation. There is, however published case law from other states that is persuasive.

The Ohio Appeals Court in Selz (a bicycle case, echoing Lott v. Smith, a published Georgia Appeals Court decision involving a corn combine) concluded that “impeding traffic” is to be interpreted as “deliberately travelling at a reduced speed”, rather than “travelling below the maximum speed limit”. Indeed, many things might cause other traffic to slow, but are commonly accepted and not considered “impeding”, including: left turns, pulling a heavy load, driving at some a speed other than “the maximum speed limit plus grace margin” and operation of a farm/construction vehicle, plows or other vehicles the primary purpose of which isn’t transportation.
references: State v. Selz [2000], 139 Ohio App.3d 947,  Lott v. Smith (1980), 156 Ga. App. 826 275 S.E.2d 720.

Speaking of implements of husbandry; I was surprised to see this out and about in Tempe in spring of 2019…

Special speed limitations

I would venture to say that 10mph maximum is often going to be slower than the normal speed of traffic…

§28-706. Special speed limitations
A. A person shall not drive a vehicle equipped with solid rubber or cushion tires at a speed of more than ten miles per hour.

At first I was thinking solid rubber or cushion tires was just some sort of old-timey thing, but as it turns out they are in use in modern forklifts as well as some other construction/maintenance, and farm  equipment; of the sort that is legally allowed on public roads when being moved “incidentally”.

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For a handy compendium of Arizona Revised Statute’s speed-related laws see speed-limit/#laws

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The topic of slow moving vehicles is treated very well in an article by Steven Goodridge at iamtraffic.org relating to Crossing The Yellow Line, as in when faster traffic passes slower traffic:

Yet low-speed vehicles did not disappear from the roadways. Bicycles, thought by many in the mid-20th century to be obsolete, suitable only as children’s toys, later resurged as an economical, healthy, energy-efficient travel mode. Mopeds and scooters continued to be used as an affordable alternative to motorcycles. Horse-drawn carriages remained in use by traditionalist groups and equestrian tour operators. Tractors and construction vehicles were joined by new types of short-range electric utility vehicles. Laws throughout the country recognize a general right to travel on public roadways. At I Am Traffic, we are aware of some troubling infringements on this right, but the law does generally recognize that the public’s right to the road is not dependent on speed capability.

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Various

This was reported in late 2017, a tractor moving at average bicycle speed, significantly slower than the 45mph maximum speed limit… there was no horn blowing, no wild gesticulating, no screaming, no assaults, no 911 calls. After the bend the drivers wanting to go faster passed the slow moving vehicle by changing lanes without incident.

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