Chat GPT Query: Using the 2016 study “The cost-effectiveness of bike lanes in New York City,” Jing Gu, Babak, Peter Alexander Muennig, Mailman School of Health, 8/10/2016,  … model the cost effectiveness of the Grayways proposal to designate weekend recreational network in New York City.

Chat GPT Response: Here’s a structured cost-effectiveness model for the proposed Grayways weekend recreational network in New York City, based on the framework and findings of the 2016 study “The cost-effectiveness of bike lanes in New York City” by Gu, Mohit, and Muennig (Mailman School of Public Health, 2016). 

📌 1. Summary of the Baseline Study

The original 2016 study modeled New York City’s investment of $8.1 million in bike lane infrastructure (45.5 miles)and used a two-stage economic model (regression + Markov health model) to estimate:

• a 9.32% increase in cycling probability from that investment, and
• 2.2 additional QALYs (quality-adjusted life years) per 1,000 residents over a lifetime of NYC citizens,
• at a net incremental cost of ~$1,297 per QALY gained (with a possible range of –$544 to $5,038 per QALY). 

This means the investment was highly cost-effective by typical public health standards (often referenced at ~$50,000–$150,000 per QALY). 

📌 2. What Grayways Is

The Grayways proposal calls for a 500-mile weekend recreational cycling network across the Bronx, Brooklyn, Queens, and Staten Island. It would:

• Use existing bikeways, quiet residential streets, and under-utilized industrial areas on weekends,
• Connect parks and playgrounds with regular rest nodes, and
• Rely initially on GPS wayfinding and street designations rather than heavy capital construction. 

Unlike dedicated bike lanes constructed by NYC DOT, Grayways emphasizes low-stress, mostly low-cost repurposing of existing infrastructure.

📌 3. Adapting the Bike Lane Model to Grayways

To model Grayways’ cost-effectiveness, we adapt the analytical framework of the 2016 study:

A. Inputs & Assumptions

Variable	Bike Lane Study	Grayways Equivalent (Model)
Investment	$8.1M for 45.5 miles of bike lanes	Assumed $5M–$20M for signage, safety upgrades, wayfinding, marketing
Network Size	45.5 miles	500 miles
Ridership Increase	9.32% per 45.5 miles	Expected lower per-mile increase due to lower physical separation
QALYs Gained	~0.0022 per person citywide	Scaled projection below

Why higher cost range for Grayways? Because while Grayways uses cheaper infrastructure, scaling to 500 miles still requires signage, traffic calming, and some targeted improvements to reach broader public uptake.

B. Ridership Uptake Estimate

The original study’s regression suggests about 0.2% increase in cycling probability per mile of bike lane (9.32%/45.5). If Grayways effectively activates 500 miles of network, one might project up to ~10% incremental increase in cycling participation citywide—similar in magnitude to the baseline study but spread over a much larger network.

(This assumes marginal returns diminish beyond core urban routes, a common pattern in transportation economics.)

C. Health & Environmental Benefits (QALYs)

Using the original per-mile estimate:

• For 45.5 miles: ~0.0022 QALYs gained per person citywide;
• For 500 miles: scaling roughly by mileage suggests ~0.024 QALYs gained per person over a lifetime—assuming Gazewise achieves similar relative ridership, safety, and physical activity effects.

This is a rough projection, not a full microsimulation.

D. Costs & Cost-Effectiveness Ratio

If Grayways cost:

• Low Estimate: $5M total → ~$10 per mile of network
• High Estimate: $20M total → ~$40 per mile

Then the cost per QALY (assuming similar health benefit per mile as fixed lanes) might be approximated:

This range is well below $1,300/QALY found in the bike lane study, suggesting Grayways could be equally or even more cost-effective. The lower bound also reflects that weekday physical infrastructure costs were avoided by using low-stress streets and GPS wayfinding first.

📌 4. Why Grayways Could Be Cost-Effective

Key reasons:

1. Lower Capital Cost: Uses existing rights-of-way and simple signage, rather than pavement or curb redesign.
2. Broader Network Scale: Provides recreational space across all boroughs, potentially spreading health benefits more equitably.
3. Weekend Activation: Targets times when streets are under-utilized anyway, minimizing traffic conflicts and management costs.
4. Incremental Safety Improvements: Can be upgraded over time, possibly increasing uptake and reducing per-mile cost.

Even given uncertainty in ridership changes and adaptation, the model points to a likely cost per QALY well within the range of the original study’s outcome and highly favorable compared to many public health interventions. 

📌 5. Limitations & Uncertainties

This model is a projected adaptation, not a full empirical simulation. Uncertainties include:

• Realized cycling uptake across a diverse network;
• Safety outcomes on low-traffic but not fully separated roadways;
• Behavioral responses and broader economic impacts (e.g., tourism, retail).

To get a more precise estimate, one would need a full Markov model similar to the original study, calibrated for Graywaysspecific route characteristics and costs.

📌 6. Conclusion

Based on the structure of the 2016 study and plausible assumptions about Grayways:

Designation of a weekend recreational network across NYC could be highly cost-effective in public health terms, potentially delivering QALYs at a cost in the hundreds (not thousands) of dollars per QALY gained—assuming modest increases in cycling activity and relatively low implementation costs.

This suggests that Grayways—if executed thoughtfully—could rival or outperform the cost-effectiveness of traditional bike lane investments shown in the baseline study.