Issues & Analyses: Dark Skies And Safe Roads. Can We Have Both?  (Part 2)

Would you walk, bike, or take the bus in Amherst at night? What about in foggy, rainy, snowy, or smoky weather?  If not, what would it take for you to do so? These are crucial questions to ask if we want to achieve a transportation mode shift in Amherst toward sustainable, equitable modes of transportation like walking, biking, and transit.

When these kinds of questions have been asked in public forums or in assessments of street conditions in Amherst, one of the repeated recommendations is: more and better streetlighting. This was a recommendation in the 2015 Amherst Transportation Plan, the 2019 Amherst Bicycle and Pedestrian Network Plan, and 2018 recommendations from the transportation subcommittee after their walking tours of North Pleasant, East Pleasant, and Echo Hill (also suggested in the subcommittee’s fourth walking tour, of Shays and Pomeroy Streets). The need for lighting for pedestrians and bicyclists is also mentioned in the 2012 Amherst Master Plan’s transportation chapter .

This is Part 2 in a 3-part series on streetlights in Amherst. This week I ask why and how could more and better streetlighting encourage people to bike, walk, and take the bus at night or in bad weather? What would this lighting look like in practice? And, can we get more and better streetlighting while town councilors are trying to reduce  it in their streetlights policy proposal?  What kind of streetlighting would support safer walking, biking, and transit use, as well as a transportation mode shift. I also build from Part 1 of this series, which analyzed the streetlights proposal, to outline the kind of lighting that might be ideal to support both transportation goals and the goals of nighttime light reduction. The final section in this week’s column describes some of the practical challenges to achieving that ideal in Amherst. In two weeks I’ll wrap up  the series with an outline of the kind of Amherst policy that could address both goals while dealing effectively with challenges and tradeoffs.

As before, I focus especially on the “arterial” or connector roads—crucial through-routes for pedestrians and bicyclists and often locations of bus stops. I summarize technical information using diagrams.

Recap from Part 1 (visual summary)
To provide an easy visual comparison, I am copying the two summary diagrams I developed for the previous column, Part 1 of this streetlights series. The first shows an “arterial,” “collector,” or connector street in Amherst under current streetlighting conditions; the second shows the same street under the proposed streetlights policy.

Figure 1. Current conditions on a typical Amherst arterial street, as well as on many neighborhood through-streets. Both light pollution and safety lighting need improvement. Figure by Eve Vogel.

Figure 2: The same arterial street under the proposed streetlights policy. The policy solves night sky and light pollution problems at the expense of safety and a transportation mode shift. Figure by Eve Vogel.

What Kind Of Streetlighting Can Encourage People To Bike, Walk, And Take The Bus?
Well-placed streetlights provide three major benefits to improve walking, biking, transit, and other kinds of micromobility and aided mobility. First, they make people and vehicles more visible. This allows other road users to see them and steer around or away from them.  Second, they help road users to see where they are going. Seeing the path in front of you is particularly crucial for anyone moving fast (car drivers, of course, but also bicyclists, scooters, and others) and anyone vulnerable to falling (e.g. older adults using a walker or cane). Third, streetlights shift people’s perceptions of an area: they help people feel safe, and they can provide a welcoming, pleasant ambiance. This third benefit, it turns out, is crucial for a transportation mode shift. Only if perceptions change will the large portion of travelers who in theory could bike, walk, or take the bus (or get around using other micromobility devices like scooters, or mobility aids like walkers and wheelchairs), choose to do so.

But what kind of lighting, and where, is best for these purposes—and does it really need to glare into our eyes, shine into our yards, and white out the night sky? 

Here the streetlights proposal provides an opportunity. The specific performance standards in the streetlights policy appendix invite a set of equally specific performance standards for safety for pedestrians, bicyclists, transit users, and other users of non-car-and-truck modes of transportation. That then can be compared with the specifics of the streetlights proposal to uncover win-win options as well as conflicts and tradeoffs.

To uncover performance standards for walking, bicycling, and transit, I consulted various sources, primarily the Federal Highway Administration (FHA) 2022 Pedestrian Lighting Primer. (See also this research study that informed the primer.) Transit users are of course also pedestrians, for whom certain locations and routes are crucial (and often dangerous) for waiting, getting on and off, crossing streets, and going to and from transit stops. The pedestrian primer takes these into account. There is nothing so comprehensive for streetlighting for bicyclists so I gleaned information from several sources, including Schreder FOCUS, which cites EU standards, and FHA’s BikeSafe. (I could not use NACTO’s next-generation design guide for bikeways, as it’s not due until 2024; the current edition has little on lighting.)

I compiled what I thought were the most important and relevant of these design standards for Amherst. I have posted that list on the web . Below I summarize these for readers with a diagram, Figure 3. As in Figures 1 and 2 in last week’s column, Figure 3 represents an arterial or connector street like North Pleasant north of campus, East Hadley Road, or West Street—or a neighborhood through-street like Heatherstone Road. (As before, imagine your favorite.) The road has shoulders or sidewalks on both sides. Now, the streetscape is lit up well for pedestrian, bicyclist, and transit user safety and confidence.

Figure 3. Street Lighting that could keep pedestrians, bicyclists, and transit users safe, and promote a transportation mode shift. Figure by Eve Vogel.

The diagram illustrates several key aspects of the pedestrian, transit, and bicyclist safety performance standards.  There is fairly consistent lighting along the whole route. Because of this, all three pedestrians and both bicyclists in the figure are easily visible, and the way in front of them is well lit. The road itself reflects some light, and the paint stripes on the road are bright and easily visible. The shoulders or sidewalks are both lit, and the light extends past their edges to provide a light buffer beyond the sidewalk or shoulder–increasing pedestrians’ and bicyclists’ visibility to drivers and their sense of safety. A spotlight lights up the bus stop and the crosswalk, so that even in the glare of the bus’s headlights or other oncoming cars, the pedestrian headed for the bus stop is easy to see, and can see the path in front of him. 

The safety performance standards do not require light to extend everywhere, nor to be excessively bright. Not too far above the top of the bus, the light quickly begins to fade, and it is dark above that. Though the light extends past the edges of the sidewalks or shoulders, it fades significantly by about a half-roadway-width beyond the road. 

Luminance vs. Illuminance
The safety standards also don’t dictate the locations of most streetlights, which is why they are not shown, except for one implied in the spotlight. The location or brightness of the streetlights is important only indirectly, as it affects how much light there is and what is lit up. The pedestrian lighting standards provide numbers both for illuminance, or how much light reaches a surface and also for luminance, how much light reflects off a surface—a surface such as a sidewalk or a pedestrian. This contrasts with the night-sky performance standards which prioritize standards only for illuminance, or how much light reaches a surface.

Under the pedestrian and bicycle safety standards, different locations and routes need different luminance. The main factors that determine the needed illuminance and luminance are: how many vehicles or travelers use the route at night; how close pedestrians and bicyclists are to cars in the roadway; how fast the traffic is going; and whether that particular location or that kind of location is particularly dangerous. For example: a sidewalk with a lot of night-time pedestrians needs to have more light. In Amherst, this would include downtown sidewalks and probably a few other routes such as North Pleasant north of campus; the latter is doubly indicated because it has a high rate of crashes. Travelers in a shoulder or an on-road bike lane—for example, the northern half of East Pleasant– need more light and to look brighter than those on a separated sidewalk.  If the traffic speed is 25 mph or faster, objects need to be brighter, as at that speed, a pedestrian or bicyclist who is hit by a car is likely to die. Almost every connector road and neighborhood through-street in Amherst exceeds this speed criterion. Finally, there are certain locations that are predictably more dangerous for pedestrians, bicyclists, and transit users, where extra light is needed. These include intersections, bus stops, sharp curves and dips, and crosswalks. 

For both luminance and illuminance it is crucial that the angle of the light is correct, as poorly placed light can create glare or backlighting, making objects look darker, not lighter. Lower-height lights, for example, can provide an inviting ambiance, but they may be more likely to shine in pedestrians’ eyes, especially if their light is used to extend out far, in an almost horizontal direction. This kind of lighting can reduce visibility. In this diagram I have avoided the question of where lights need to go, by showing only the luminance effects.

In the diagram, most of the light is white—and it is bright white at the bus stop and crosswalk. Pedestrian safety standards suggest a color spectrum range of 3000 to 4000 Kelvin, a neutral or white light, as a good balance. It makes sense that on the edges, light might be warmer. I drew the edges where light may extend slightly into people’s yards slightly on the yellowish side.

What are the benefits of using streetlights to meet these kinds of safety standards? There will be significantly reduced crashes, injuries and fatalities; and many more people will feel safe and confident walking, biking, and busing at night, supporting a mode shift.

The problems and challenges? The light in the margin adjacent to the shoulder or sidewalk may be undesirable for property owners and viewers of the night sky. Even more problematic, continuous lighting suggests a lot of lights. That could produce considerable light “trespass,” and it’s also likely outside the Town budget.

A Possibly Ideal Compromise: Solving The Problems Of Light Pollution And Safety Though Without Accounting For Cost
What kind of lighting could best both 1) protect the night skies and limit light pollution; and 2) protect pedestrians, bicyclists, and transit users, and promote a transportation mode shift? 

There is a best-of-both-worlds. It would look something like this:

Figure 4. A close-to-ideal streetscape for reduced light pollution; pedestrian, bicyclist, and transit user safety; and a mode shift. Figure by Eve Vogel.

In Figure 4, a best-of-both-worlds example, the night sky is more visible than under current conditions (Figure 1), and human and animal eyes are less strained. That is because upward-directed light and glare are much reduced, and most of the lighting is in the warmer end of the spectrum. These benefits replicate the benefits from the current streetlights policy proposal (Figure 2). An addition here compared to Figure 2 is that the lights are mounted at a lower height, further reducing light shining into neighboring properties and into the night sky.

Safety is also significantly improved compared to current conditions (Figure 1), and so is the sense of safety and comfort that will contribute to a mode shift. As in the diagram based on pedestrian and bicycles safety standards (Figure 3), the three pedestrians and two bicyclists are all visible, and all have enough light to see the path in front of them. The spotlight over the bus stop and crosswalk makes the pedestrian there especially visible, even in the glare of the bus’s headlights. The 15-foot-high lights are pedestrian-scale; combined with the warm but still bright-enough slightly yellowish light, the area is inviting and comfortable, supporting a transportation mode shift to walking, biking, and transit.

The diagram represents both win-win solutions, and compromises to deal with tradeoffs.

A key win-win comes from lowering the height of the lamps to 15 feet. This reduces light into the night sky and neighboring properties, and at the same time provides pedestrian-scale lighting that is inviting and comfortable, encouraging walking, bicycling, and busing. A second win-win is the bright paint on the crosswalk and roadway which provides excellent luminance on the road surface from car headlights, even where there is less streetlight. 

A key compromise is between the illumination, color, and frequency of lights. In this diagram, the streetlights meet the performance standards of the proposed streetlights policy. This means less light out to the sides onto neighboring property, less interference with the night sky, and a yellowish light that is less irritating to human and animal eyes and brains. But it also means a single light cannot light up as far along or across a roadway or sidewalk. To compensate for the smaller lit area, more streetlights are used. The multiple streetlights are spaced as far apart as they can be while still providing for adequate luminance of the pedestrians and bicyclists. This spacing means that the light is not as continuous as in Figure 3 under the safety performance standards, but it is continuous enough that these travelers can see and be seen. 

Another compromise is that streetlights are yellow-white, while spotlights over bus stops and crosswalks are a brighter white. A third compromise is that some light “trespass” on adjacent property is realized. Together these mean that while the light color prioritizes the night sky, the lit area prioritizes safety. 

Now, back to our initial question. If our arterial or connector streets, or your neighborhood through-streets, had streetscapes that looked like those in Figure 4, would you walk, bike, or take the bus in Amherst at night? What about in foggy, rainy, snowy, or smoky weather?  

I’m guessing that a significant percentage of you would walk or bike or take the bus far more often and more readily than you do now. I believe this kind of streetscape on our connector roads would advance a mode shift in Amherst.

Three-way Tradeoffs: Toward A Town Policy That Can Function Within Cost Constraints, Protect The Night Sky, And Support A Transportation Mode Shift
So, what’s the problem? Why don’t we do this everywhere? One key problem is that to do this along every arterial or connector or neighborhood through-street in Amherst would be cost prohibitive. As explained in Part 1, most streetlights are mounted on utility poles to save money, and those are required (by the utility) to be mounted high up. In other words, it turns out there is not simply a two-way tradeoff between night sky and safety, but a three-way tradeoff among night sky, safety, and cost. 

A second problem is that different streets and contexts across Amherst call for different compromises.

The good news is that the analysis thus far will enable us to add in questions of cost and geographic variability across the town’s arterials, connectors, and neighborhood through-streets.  We’ll be able to think clearly about how to manage the three-way tradeoffs among night sky, safety, and cost into a workable town policy.  That will be the topic for Part 3 of this series, in two weeks.