G: TL;DR: Yes—there’s a lot of research. In short, (a) signal spacing / block length and (b) the speed you coordinate for (often close to but not always the posted speed) jointly determine whether traffic “platoons” move in waves with usable gaps between them. Closer spacing and/or badly chosen coordination speeds create more stops, fewer gaps, and tougher unsignalized turns. Wider spacing (to a point), clean access spacing, and well-set offsets grow the green “bandwidth,” keep speeds steadier, and make those between-platoon gaps big enough to turn across traffic. citeturn0search19turn0search13turn0search5

What studies actually say

Useful spacing bands (rules of thumb). FHWA’s Signal Timing Manual notes that for most arterials, 500 ft–0.5 mi spacing is where coordination really pays off; at higher speeds you can space signals up to ~1 mile and still coordinate well; very close spacing (<500 ft) usually forces you to manage queues rather than progression (i.e., you sacrifice green waves, which also kills usable turning gaps). citeturn0search19
Minimum spacing that helps speed. A 2024 urban-arterial speed study found that having ≥0.2 miles (~1,050 ft) between signals/stop-controls tended to improve operating speeds—a quantified threshold that lines up with practice. citeturn0search7
Irregular or short spacings = more stops, lower arterial speed. Classic coordination research and guidance show that closely or unevenly spaced signals increase stops and reduce through speed; modern HCM methods explicitly penalize mid-block “segment running time” when spacing is short. citeturn0search17turn0search5
Progression math (why gaps appear…or vanish). Favorable progression happens when the proportion arriving on green (PVG) is greater than the green ratio (g/C)—that’s when you get real “bandwidth” and predictable gaps between platoons. Those gaps are exactly what side-street/driveway turners need; get the offsets or coordination speed wrong and PVG drops, platoons smear together, and gaps disappear. citeturn0search9turn0search13
Speed, variability, and safety. On multi-signal arterials, studies show signal spacing affects mean speeds and speed variation, and higher speed variation correlates with more crashes—one reason steady, well-coordinated progression is a safety as well as an operations win. citeturn0search26
Access density (turn opportunities) matters a lot. Corridor-level evaluations by FHWA/NCHRP consistently find that more driveways/unsignalized openings per mile raise crash rates and disrupt flow; access-management treatments (fewer full-movement driveways, right-in/right-out with downstream U-turn, better corner clearance) improve safety and operations. U-turn-based designs at unsignalized medians, when applied correctly, have been shown to operate safely and effectively. citeturn0search12turn0search20turn0search16turn0search23

Practical takeaways (you can picture these on your corridor)

If signals are too close (<500 ft): expect queue spillbacks and weak green-wave effects; turning across traffic becomes hard because platoons keep arriving without healthy gaps. citeturn0search19
Around 0.2–0.5 mi spacing with a coordinated progression speed matched to the corridor (often near the posted speed, sometimes a little lower) you get stronger platoons and longer inter-platoon gaps—that’s when mid-block turns are most feasible. citeturn0search7turn0search21
At higher posted speeds (e.g., 45 mph suburban arterials), longer spacing (½–1 mi) can still coordinate well, often with longer cycles—again producing predictable gaps between waves. citeturn0search19
Irregular block lengths complicate offsets; dispersion between signals eats your bandwidth. The fix is better offsets or, if geometry is baked in, access consolidation so fewer people must turn across the stream mid-block. citeturn0search13turn0search5

Why your unsignalized turn sometimes felt “nearly impossible”

When a corridor is coordinated for through traffic, vehicles leave each upstream signal in platoons. If the green waves and offsets are tuned tightly (or if spacing is short/uneven), those platoons can overlap, leaving very few usable gaps at your driveway or side street. Change the offsets—or widen spacing / reduce access points—and usable gaps reappear between platoons. citeturn0search13turn0search19

Design/ops levers agencies use

Pick a coordination speed and cycle that fit the spacing (Signal Timing Manual / HCM methods), then set offsets to maximize PVG and bandwidth. citeturn0search21turn0search9
Target ≥0.2 mi spacing where possible and avoid irregular very-short links. citeturn0search7
Access management near intersections and mid-block: consolidate/close or convert to right-in/right-out + downstream U-turn, increase corner clearance, and add medians to cut conflict points while keeping circulation viable. citeturn0search20turn0search16

If you want, tell me a typical posted speed and approximate block length you see on the corridor you’re thinking of, and I’ll sketch a quick, numbers-based scenario (cycle length, progression speed, expected platoon headways) to show when those turns will feel easy vs impossible.