Radius vs. Drive-Time Targeting: Which Delivers Better Clinical Trial Leads

A 15-mile radius around a clinical research site in downtown Chicago includes patients who are 15 minutes away and patients who are 55 minutes away — because 15 miles in an urban grid means very different things depending on direction and traffic. Drive-time targeting solves this by defining your catchment area based on how long it actually takes to get to your site, not how far away someone is in a straight line. For most clinical research sites, switching from radius to drive-time targeting improves lead quality by 20–35% with no increase in ad spend.

How Radius Targeting Creates Hidden Geographic Waste

Radius targeting draws a circle. In suburban or rural markets where roads are direct and traffic is light, a 20-mile radius is a reasonable approximation of a 20-minute drive. In urban markets, a 10-mile radius can include neighborhoods that are 45 minutes away by road. Patients in those neighborhoods are 3–4x more likely to miss appointments and withdraw than patients who can reach your site in 15 minutes. You are paying equal rates to advertise to both groups.

How Drive-Time Targeting Works in Google Ads

Google Ads supports drive-time targeting through the “Areas near” option combined with location extensions. More precisely, it is implemented through a combination of radius targeting and bid adjustments informed by traffic data. Google’s Performance Max campaigns have native drive-time signal incorporation. For Search campaigns, the most accurate drive-time approach uses multiple layered radius targets with bid modifiers: full bid at 0–10 minutes (innermost radius), minus 20% at 10–20 minutes, minus 40% at 20–30 minutes, excluded beyond 30 minutes.

Setting Up Layered Radius Targeting with Bid Modifiers

In Google Ads:

1. Campaigns → your campaign → Locations → Add location → enter your site address → select radius → set to 10 miles → Save.
2. Add a second radius at 20 miles. Add a third at 30 miles.
3. For each radius layer, set a bid adjustment: inner radius +20%, middle radius 0%, outer radius -30%.
4. Google will automatically apply higher bids to patients in the inner ring and discounted bids to patients in the outer ring — approximating drive-time weighting through overlapping radius layers.

This is the closest approximation to true drive-time targeting available in the standard Google Ads interface without third-party tools.

When Radius Targeting Is Still the Right Choice

Radius targeting remains more appropriate in two scenarios: (1) rural markets where roads are direct and drive time correlates closely with distance, and (2) sites where most patients walk or use public transit. In transit-heavy urban markets, a walking-time or transit-time model is more predictive of dropout than either radius or drive time. In these cases, target by transit zone or neighborhood rather than distance.

Comparing Your Results: A 30-Day Test Protocol

Run drive-time layered targeting and simple radius targeting simultaneously in separate ad groups for 30 days. Track: cost-per-inquiry, inquiry-to-screened-visit rate, and screened-to-enrolled rate by group. The group with the better cost-per-enrolled-patient wins. Most sites find drive-time layering wins by 20–35% on cost-per-enrolled in urban and suburban markets.

48-Hour Action List

1. Hour 1: Open Google Maps. Drop a pin at your site address. Use the “Directions” feature to measure actual drive time to your current campaign radius boundary at 8 AM on a Tuesday — peak commute time, which approximates participant visit conditions. Record the drive time at multiple points on your radius boundary.
2. Hour 2: In Google Ads, duplicate your best-performing search campaign. In the copy, replace the single radius with three layered radii at 10, 20, and 30 miles with bid modifiers of +20%, 0%, and -30% respectively.
3. Hour 3: Label the original campaign “Radius Test” and the duplicate “Drive-Time Test” using campaign labels. Set equal budgets. Run both for 30 days.
4. Day 2: Set a 30-day calendar reminder to compare cost-per-inquiry and inquiry-to-screened rate between the two campaigns. Pause the underperformer and scale the winner.