Transmit power falls off rapidly with distance. In the
free-space model, doubling the range decreases the
delivered power by a factor of four (square law). Yes,
the base station is transmitting more power, but it is
also much farther away than the handset.
In this
(
http://cpk.auc.dk/antennas/pub/ExposureWCDMA.pdf)
study of W-CDMA hazards, they estimate of 1/8 of 1W for
the handset and 20W per user for the base station. If you
assume an average of 100 users, that would be 16,000
times more power at the base, but the handset is only
10cm from your face! 10cm * sqrt(16,000) = 12.6m.
So, if you are more than 12.6m from the tower antenna
the field from the handset is worse. In the paper, they
cite a safety distance of 3 to 4.5m (Sec 3.2.1). They also
point out at the end of section 2 that the allowed
downlink field for W-CDMA is greater than for GSM.
Worry about your own handset before the tower. Worry
most about the person piloting the truck / SUV while
talking on their handset.
--Shaun