STOCK-BASED COMPENSATION

As of March 31, 2019, the Company maintains employee stock-based compensation plans for stock options, restricted stock, and incentive stock units as governed by the 2011 Stock Incentive Compensation Plan, as amended and restated (the “2011 Plan”) and the 2000 Stock Incentive Plan, as amended (the “2000 Plan”). The 2011 Plan has a term through May 10, 2027 and provides a maximum of 3,800,000 shares for grants or awards, plus any shares which remain available under the 2000 Plan. The amendment and restatement of the 2011 Plan was approved by stockholders of Wabtec on May 10, 2017. The Company also maintains a 1995 Non-Employee Directors’ Fee and Stock Option Plan as amended and restated (“the Directors Plan”).

Stock-based compensation expense was $8.5 million and $5.7 million for the three months ended March 31, 2019 and 2018, respectively. Included in stock-based compensation expense for the three months ended March 31, 2019 is $0.4 million of expense related to stock options, $2.7 million related to restricted stock, $0.8 million related to restricted stock units, $4.3 million related to incentive stock units and $0.3 million related to units issued for Directors’ fees. At March 31, 2019, unamortized compensation expense related to stock options, non-vested restricted shares and incentive stock units expected to vest totaled $75.6 million.

Stock Options Stock options are granted to eligible employees at an exercise price equivalent to the stock's fair market value, which is the average of the high and low Wabtec stock price on the date of grant. Under the 2011 Plan and the 2000 Plan, options granted prior to 2019 become exercisable over a four-year vesting period, while options granted in 2019 become exercisable over a three-year vesting period. Both vesting periods expire 10 years from the date of grant.

The following table summarizes the Company’s stock option activity and related information for the 2011 Plan, the 2000 Plan and the Directors Plan for the three months ended March 31, 2019:



	Options		Weighted Average Exercise Price		Weighted Average Remaining Contractual Life	Aggregate Intrinsic value (in thousands)
Outstanding at December 31, 2018	466,677		$	61.04	5.7	$	5,917
Granted	128,555		72.85			112
Exercised	(734	)	64.54			7
Canceled	(228	)	74.38			—
Outstanding at March 31, 2019	594,270		63.58		6.4	6,027
Exercisable at March 31, 2019	355,222		56.00		5.2	6,295

The fair value of each option grant is estimated on the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:



	Three Months Ended March 31,
	2019		2018
Dividend yield	0.66	%	0.33	%
Risk-free interest rate	2.63	%	2.70	%
Stock price volatility	25.8	%	23.9	%
Expected life (years)	5.0		5.0

The dividend yield is based on the Company’s dividend rate and the current market price of the underlying common stock at the date of grant. Expected life in years is determined from historical stock option exercise data. Expected volatility is based on the historical volatility of the Company’s stock. The risk-free interest rate is based on the U.S. Treasury bond rates for the expected life of the option.

Restricted Stock, Restricted Units and Incentive Stock Beginning in 2006, the Company adopted a restricted stock program. As provided for under the 2011 Plan and 2000 Plan, eligible employees are granted restricted stock that generally vests over four years from the date of grant. Under the Directors Plan, restricted stock units vest one year from the date of grant.

In addition, the Company has issued incentive stock units to eligible employees that vest upon attainment of certain cumulative three-year performance goals. Based on the Company’s performance for each three-year period then ended, the incentive stock units can vest, with underlying shares of common stock being awarded in an amount ranging from 0% to 200% of the amount of initial incentive stock units granted. The incentive stock units included in the table below represent the number of incentive stock units that are expected to vest based on the Company’s estimate for meeting those established performance targets. As of March 31, 2019, the Company estimates that it will achieve 100%, 100% and 100% for the incentive stock awards expected to vest based on performance for the three-year periods ending December 31, 2019, 2020, and 2021, respectively, and has recorded incentive compensation expense accordingly. If our estimate of the number of these incentive stock units expected to vest changes in a future accounting period, cumulative compensation expense could increase or decrease and will be recognized in the current period for the elapsed portion of the vesting period and would change future expense for the remaining vesting period.

Compensation expense for the non-vested restricted stock and incentive stock units is based on the average of the high and low Wabtec stock price on the date of grant and recognized over the applicable vesting period.

The following table summarizes the restricted stock activity and related information for the 2011 Plan, the 2000 Plan and the Directors Plan, and incentive stock units activity for the 2011 Plan and the 2000 Plan with related information for the three months ended March 31, 2019:



	Restricted Stock and Units		Incentive Stock Units		Weighted Average Grant Date Fair Value
Outstanding at December 31, 2018	445,089		415,243		$	75.51
Granted	535,873		258,600		70.64
Vested	(105,651	)	(119,835	)	68.62
Adjustment for incentive stock awards expected to vest	—		18,398		81.20
Canceled	(6,733	)	(5,350	)	80.17
Outstanding at March 31, 2019	868,578		567,056		73.93