  Cosmic acceleration is investigated through a kink-like expression for the
deceleration parameter (q). The new parametrization depends on the initial
(q_i) and final (q_f) values of q, on the redshift of the transition from
deceleration to acceleration (z_{t}) and the width of such transition (\tau).
We show that although supernovae (SN) observations (Gold182 and SNLS data
samples) indicate, at high confidence, that a transition occurred in the past
(z_{t}>0) they do not, by themselves, impose strong constraints on the maximum
value of z_{t}. However, when we combine SN with the measurements of the ratio
between the comoving distance to the last scattering surface and the
SDSS+2dfGRS BAO distance scale (S_{k}/D_{v}) we obtain, at 95.4% confidence
level, z_{t}=0.84+{0.17}-{0.13} and \tau =0.51-{0.17}+{0.23} for
(S_{k}/D_{v}+Gold182), and z_{t}=0.88-{0.10}+{0.12} and \tau
=0.35-{0.10}+{0.12} for (S_{k}/D_{v} + SNLS), assuming q_i=0.5 and q_f=-1. We
also analyze the general case, q_f\in(-\infty,0) finding the constraints that
the combined tests (S_{k}/D_{v} + SNLS) impose on the present value of the
deceleration parameter (q_0).
